diff --git a/src/lib/es2018.intl.d.ts b/src/lib/es2018.intl.d.ts
index 9dfc84ed364de..8e0a27fe965d4 100644
--- a/src/lib/es2018.intl.d.ts
+++ b/src/lib/es2018.intl.d.ts
@@ -29,12 +29,13 @@ declare namespace Intl {
         select(n: number): LDMLPluralRule;
     }
 
-    const PluralRules: {
+    interface PluralRulesConstructor {
         new (locales?: string | string[], options?: PluralRulesOptions): PluralRules;
         (locales?: string | string[], options?: PluralRulesOptions): PluralRules;
-
         supportedLocalesOf(locales: string | string[], options?: { localeMatcher?: "lookup" | "best fit"; }): string[];
-    };
+    }
+
+    const PluralRules: PluralRulesConstructor;
 
     // We can only have one definition for 'type' in TypeScript, and so you can learn where the keys come from here:
     type ES2018NumberFormatPartType = "literal" | "nan" | "infinity" | "percent" | "integer" | "group" | "decimal" | "fraction" | "plusSign" | "minusSign" | "percentSign" | "currency" | "code" | "symbol" | "name";
diff --git a/src/lib/es2020.intl.d.ts b/src/lib/es2020.intl.d.ts
index 550edaaa6c848..d63508249ddcb 100644
--- a/src/lib/es2020.intl.d.ts
+++ b/src/lib/es2020.intl.d.ts
@@ -1,9 +1,11 @@
 /// <reference lib="es2018.intl" />
 declare namespace Intl {
     /**
-     * [Unicode BCP 47 Locale Identifiers](https://unicode.org/reports/tr35/#Unicode_Language_and_Locale_Identifiers) definition.
+     * A string that is a valid [Unicode BCP 47 Locale Identifier](https://unicode.org/reports/tr35/#Unicode_locale_identifier).
      *
-     * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl#locales_argument).
+     * For example: "fa", "es-MX", "zh-Hant-TW".
+     *
+     * See [MDN - Intl - locales argument](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl#locales_argument).
      */
     type UnicodeBCP47LocaleIdentifier = string;
 
@@ -71,16 +73,9 @@ declare namespace Intl {
     type RelativeTimeFormatStyle = "long" | "short" | "narrow";
 
     /**
-     * [BCP 47 language tag](http://tools.ietf.org/html/rfc5646) definition.
+     * The locale or locales to use
      *
-     * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl#locales_argument).
-     */
-    type BCP47LanguageTag = string;
-
-    /**
-     * The locale(s) to use
-     *
-     * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl#locales_argument).
+     * See [MDN - Intl - locales argument](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl#locales_argument).
      */
     type LocalesArgument = UnicodeBCP47LocaleIdentifier | Locale | readonly (UnicodeBCP47LocaleIdentifier | Locale)[] | undefined;
 
@@ -200,7 +195,7 @@ declare namespace Intl {
          * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/RelativeTimeFormat).
          */
         new (
-            locales?: UnicodeBCP47LocaleIdentifier | UnicodeBCP47LocaleIdentifier[],
+            locales?: LocalesArgument,
             options?: RelativeTimeFormatOptions,
         ): RelativeTimeFormat;
 
@@ -223,7 +218,7 @@ declare namespace Intl {
          * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/RelativeTimeFormat/supportedLocalesOf).
          */
         supportedLocalesOf(
-            locales?: UnicodeBCP47LocaleIdentifier | UnicodeBCP47LocaleIdentifier[],
+            locales?: LocalesArgument,
             options?: RelativeTimeFormatOptions,
         ): UnicodeBCP47LocaleIdentifier[];
     };
@@ -294,7 +289,7 @@ declare namespace Intl {
         /** Attempts to remove information about the locale that would be added by calling `Locale.maximize()`. */
         minimize(): Locale;
         /** Returns the locale's full locale identifier string. */
-        toString(): BCP47LanguageTag;
+        toString(): UnicodeBCP47LocaleIdentifier;
     }
 
     /**
@@ -312,7 +307,7 @@ declare namespace Intl {
      * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/Locale).
      */
     const Locale: {
-        new (tag: BCP47LanguageTag | Locale, options?: LocaleOptions): Locale;
+        new (tag: UnicodeBCP47LocaleIdentifier | Locale, options?: LocaleOptions): Locale;
     };
 
     type DisplayNamesFallback =
@@ -406,6 +401,31 @@ declare namespace Intl {
          *
          * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/DisplayNames/supportedLocalesOf).
          */
-        supportedLocalesOf(locales?: LocalesArgument, options?: { localeMatcher?: RelativeTimeFormatLocaleMatcher; }): BCP47LanguageTag[];
+        supportedLocalesOf(locales?: LocalesArgument, options?: { localeMatcher?: RelativeTimeFormatLocaleMatcher; }): UnicodeBCP47LocaleIdentifier[];
     };
+
+    interface CollatorConstructor {
+        new (locales?: LocalesArgument, options?: CollatorOptions): Collator;
+        (locales?: LocalesArgument, options?: CollatorOptions): Collator;
+        supportedLocalesOf(locales: LocalesArgument, options?: CollatorOptions): string[];
+    }
+
+    interface DateTimeFormatConstructor {
+        new (locales?: LocalesArgument, options?: DateTimeFormatOptions): DateTimeFormat;
+        (locales?: LocalesArgument, options?: DateTimeFormatOptions): DateTimeFormat;
+        supportedLocalesOf(locales: LocalesArgument, options?: DateTimeFormatOptions): string[];
+    }
+
+    interface NumberFormatConstructor {
+        new (locales?: LocalesArgument, options?: NumberFormatOptions): NumberFormat;
+        (locales?: LocalesArgument, options?: NumberFormatOptions): NumberFormat;
+        supportedLocalesOf(locales: LocalesArgument, options?: NumberFormatOptions): string[];
+    }
+
+    interface PluralRulesConstructor {
+        new (locales?: LocalesArgument, options?: PluralRulesOptions): PluralRules;
+        (locales?: LocalesArgument, options?: PluralRulesOptions): PluralRules;
+
+        supportedLocalesOf(locales: LocalesArgument, options?: { localeMatcher?: "lookup" | "best fit"; }): string[];
+    }
 }
diff --git a/src/lib/es2020.string.d.ts b/src/lib/es2020.string.d.ts
index 382bc75595e92..1602ac7b10f01 100644
--- a/src/lib/es2020.string.d.ts
+++ b/src/lib/es2020.string.d.ts
@@ -7,4 +7,18 @@ interface String {
      * @param regexp A variable name or string literal containing the regular expression pattern and flags.
      */
     matchAll(regexp: RegExp): IterableIterator<RegExpMatchArray>;
+
+    /** Converts all alphabetic characters to lowercase, taking into account the host environment's current locale. */
+    toLocaleLowerCase(locales?: Intl.LocalesArgument): string;
+
+    /** Returns a string where all alphabetic characters have been converted to uppercase, taking into account the host environment's current locale. */
+    toLocaleUpperCase(locales?: Intl.LocalesArgument): string;
+
+    /**
+     * Determines whether two strings are equivalent in the current or specified locale.
+     * @param that String to compare to target string
+     * @param locales A locale string or array of locale strings that contain one or more language or locale tags. If you include more than one locale string, list them in descending order of priority so that the first entry is the preferred locale. If you omit this parameter, the default locale of the JavaScript runtime is used. This parameter must conform to BCP 47 standards; see the Intl.Collator object for details.
+     * @param options An object that contains one or more properties that specify comparison options. see the Intl.Collator object for details.
+     */
+    localeCompare(that: string, locales?: Intl.LocalesArgument, options?: Intl.CollatorOptions): number;
 }
diff --git a/src/lib/es2021.intl.d.ts b/src/lib/es2021.intl.d.ts
index b3835b8b1ff04..1566a7353f8dd 100644
--- a/src/lib/es2021.intl.d.ts
+++ b/src/lib/es2021.intl.d.ts
@@ -125,7 +125,7 @@ declare namespace Intl {
          *
          * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/ListFormat).
          */
-        new (locales?: BCP47LanguageTag | BCP47LanguageTag[], options?: ListFormatOptions): ListFormat;
+        new (locales?: LocalesArgument, options?: ListFormatOptions): ListFormat;
 
         /**
          * Returns an array containing those of the provided locales that are
@@ -143,6 +143,6 @@ declare namespace Intl {
          *
          * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/ListFormat/supportedLocalesOf).
          */
-        supportedLocalesOf(locales: BCP47LanguageTag | BCP47LanguageTag[], options?: Pick<ListFormatOptions, "localeMatcher">): BCP47LanguageTag[];
+        supportedLocalesOf(locales: LocalesArgument, options?: Pick<ListFormatOptions, "localeMatcher">): UnicodeBCP47LocaleIdentifier[];
     };
 }
diff --git a/src/lib/es2022.intl.d.ts b/src/lib/es2022.intl.d.ts
index 7ed03b05e07ca..3beaea6af8ddd 100644
--- a/src/lib/es2022.intl.d.ts
+++ b/src/lib/es2022.intl.d.ts
@@ -71,7 +71,7 @@ declare namespace Intl {
          *
          * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/Segmenter).
          */
-        new (locales?: BCP47LanguageTag | BCP47LanguageTag[], options?: SegmenterOptions): Segmenter;
+        new (locales?: LocalesArgument, options?: SegmenterOptions): Segmenter;
 
         /**
          * Returns an array containing those of the provided locales that are supported without having to fall back to the runtime's default locale.
@@ -85,7 +85,7 @@ declare namespace Intl {
          *
          * [MDN](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/Segmenter/supportedLocalesOf)
          */
-        supportedLocalesOf(locales: BCP47LanguageTag | BCP47LanguageTag[], options?: Pick<SegmenterOptions, "localeMatcher">): BCP47LanguageTag[];
+        supportedLocalesOf(locales: LocalesArgument, options?: Pick<SegmenterOptions, "localeMatcher">): UnicodeBCP47LocaleIdentifier[];
     };
 
     /**
diff --git a/src/lib/es5.d.ts b/src/lib/es5.d.ts
index 8065e2d3de83c..f3df23047022d 100644
--- a/src/lib/es5.d.ts
+++ b/src/lib/es5.d.ts
@@ -4400,11 +4400,14 @@ declare namespace Intl {
         compare(x: string, y: string): number;
         resolvedOptions(): ResolvedCollatorOptions;
     }
-    var Collator: {
+
+    interface CollatorConstructor {
         new (locales?: string | string[], options?: CollatorOptions): Collator;
         (locales?: string | string[], options?: CollatorOptions): Collator;
         supportedLocalesOf(locales: string | string[], options?: CollatorOptions): string[];
-    };
+    }
+
+    var Collator: CollatorConstructor;
 
     interface NumberFormatOptions {
         localeMatcher?: string | undefined;
@@ -4436,12 +4439,15 @@ declare namespace Intl {
         format(value: number): string;
         resolvedOptions(): ResolvedNumberFormatOptions;
     }
-    var NumberFormat: {
+
+    interface NumberFormatConstructor {
         new (locales?: string | string[], options?: NumberFormatOptions): NumberFormat;
         (locales?: string | string[], options?: NumberFormatOptions): NumberFormat;
         supportedLocalesOf(locales: string | string[], options?: NumberFormatOptions): string[];
         readonly prototype: NumberFormat;
-    };
+    }
+
+    var NumberFormat: NumberFormatConstructor;
 
     interface DateTimeFormatOptions {
         localeMatcher?: "best fit" | "lookup" | undefined;
@@ -4480,12 +4486,15 @@ declare namespace Intl {
         format(date?: Date | number): string;
         resolvedOptions(): ResolvedDateTimeFormatOptions;
     }
-    var DateTimeFormat: {
+
+    interface DateTimeFormatConstructor {
         new (locales?: string | string[], options?: DateTimeFormatOptions): DateTimeFormat;
         (locales?: string | string[], options?: DateTimeFormatOptions): DateTimeFormat;
         supportedLocalesOf(locales: string | string[], options?: DateTimeFormatOptions): string[];
         readonly prototype: DateTimeFormat;
-    };
+    }
+
+    var DateTimeFormat: DateTimeFormatConstructor;
 }
 
 interface String {
diff --git a/tests/baselines/reference/DateTimeFormatAndNumberFormatES2021.symbols b/tests/baselines/reference/DateTimeFormatAndNumberFormatES2021.symbols
index 43802d659323c..82aede47ba9b7 100644
--- a/tests/baselines/reference/DateTimeFormatAndNumberFormatES2021.symbols
+++ b/tests/baselines/reference/DateTimeFormatAndNumberFormatES2021.symbols
@@ -2,19 +2,19 @@
 
 === DateTimeFormatAndNumberFormatES2021.ts ===
 Intl.NumberFormat.prototype.formatRange
->Intl.NumberFormat.prototype : Symbol(prototype, Decl(lib.es5.d.ts, --, --))
+>Intl.NumberFormat.prototype : Symbol(Intl.NumberFormatConstructor.prototype, Decl(lib.es5.d.ts, --, --))
 >Intl.NumberFormat : Symbol(Intl.NumberFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.bigint.d.ts, --, --))
 >Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 3 more)
 >NumberFormat : Symbol(Intl.NumberFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.bigint.d.ts, --, --))
->prototype : Symbol(prototype, Decl(lib.es5.d.ts, --, --))
+>prototype : Symbol(Intl.NumberFormatConstructor.prototype, Decl(lib.es5.d.ts, --, --))
 
 Intl.DateTimeFormat.prototype.formatRange
 >Intl.DateTimeFormat.prototype.formatRange : Symbol(Intl.DateTimeFormat.formatRange, Decl(lib.es2021.intl.d.ts, --, --))
->Intl.DateTimeFormat.prototype : Symbol(prototype, Decl(lib.es5.d.ts, --, --))
+>Intl.DateTimeFormat.prototype : Symbol(Intl.DateTimeFormatConstructor.prototype, Decl(lib.es5.d.ts, --, --))
 >Intl.DateTimeFormat : Symbol(Intl.DateTimeFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2021.intl.d.ts, --, --))
 >Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 3 more)
 >DateTimeFormat : Symbol(Intl.DateTimeFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2021.intl.d.ts, --, --))
->prototype : Symbol(prototype, Decl(lib.es5.d.ts, --, --))
+>prototype : Symbol(Intl.DateTimeFormatConstructor.prototype, Decl(lib.es5.d.ts, --, --))
 >formatRange : Symbol(Intl.DateTimeFormat.formatRange, Decl(lib.es2021.intl.d.ts, --, --))
 
 new Intl.NumberFormat().formatRange 
diff --git a/tests/baselines/reference/DateTimeFormatAndNumberFormatES2021.types b/tests/baselines/reference/DateTimeFormatAndNumberFormatES2021.types
index 51ec4fc0d8a1c..e499924e25857 100644
--- a/tests/baselines/reference/DateTimeFormatAndNumberFormatES2021.types
+++ b/tests/baselines/reference/DateTimeFormatAndNumberFormatES2021.types
@@ -4,50 +4,50 @@
 Intl.NumberFormat.prototype.formatRange
 >Intl.NumberFormat.prototype.formatRange : any
 >Intl.NumberFormat.prototype : Intl.NumberFormat
->Intl.NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>Intl.NumberFormat : Intl.NumberFormatConstructor
 >Intl : typeof Intl
->NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>NumberFormat : Intl.NumberFormatConstructor
 >prototype : Intl.NumberFormat
 >formatRange : any
 
 Intl.DateTimeFormat.prototype.formatRange
 >Intl.DateTimeFormat.prototype.formatRange : (startDate: number | bigint | Date, endDate: number | bigint | Date) => string
 >Intl.DateTimeFormat.prototype : Intl.DateTimeFormat
->Intl.DateTimeFormat : { (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; new (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; supportedLocalesOf(locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; readonly prototype: Intl.DateTimeFormat; }
+>Intl.DateTimeFormat : Intl.DateTimeFormatConstructor
 >Intl : typeof Intl
->DateTimeFormat : { (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; new (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; supportedLocalesOf(locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; readonly prototype: Intl.DateTimeFormat; }
+>DateTimeFormat : Intl.DateTimeFormatConstructor
 >prototype : Intl.DateTimeFormat
 >formatRange : (startDate: number | bigint | Date, endDate: number | bigint | Date) => string
 
 new Intl.NumberFormat().formatRange 
 >new Intl.NumberFormat().formatRange : any
 >new Intl.NumberFormat() : Intl.NumberFormat
->Intl.NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>Intl.NumberFormat : Intl.NumberFormatConstructor
 >Intl : typeof Intl
->NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>NumberFormat : Intl.NumberFormatConstructor
 >formatRange : any
 
 new Intl.NumberFormat().formatRangeToParts
 >new Intl.NumberFormat().formatRangeToParts : any
 >new Intl.NumberFormat() : Intl.NumberFormat
->Intl.NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>Intl.NumberFormat : Intl.NumberFormatConstructor
 >Intl : typeof Intl
->NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>NumberFormat : Intl.NumberFormatConstructor
 >formatRangeToParts : any
 
 new Intl.DateTimeFormat().formatRange
 >new Intl.DateTimeFormat().formatRange : (startDate: number | bigint | Date, endDate: number | bigint | Date) => string
 >new Intl.DateTimeFormat() : Intl.DateTimeFormat
->Intl.DateTimeFormat : { (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; new (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; supportedLocalesOf(locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; readonly prototype: Intl.DateTimeFormat; }
+>Intl.DateTimeFormat : Intl.DateTimeFormatConstructor
 >Intl : typeof Intl
->DateTimeFormat : { (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; new (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; supportedLocalesOf(locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; readonly prototype: Intl.DateTimeFormat; }
+>DateTimeFormat : Intl.DateTimeFormatConstructor
 >formatRange : (startDate: number | bigint | Date, endDate: number | bigint | Date) => string
 
 new Intl.DateTimeFormat().formatRangeToParts
 >new Intl.DateTimeFormat().formatRangeToParts : (startDate: number | bigint | Date, endDate: number | bigint | Date) => Intl.DateTimeRangeFormatPart[]
 >new Intl.DateTimeFormat() : Intl.DateTimeFormat
->Intl.DateTimeFormat : { (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; new (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; supportedLocalesOf(locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; readonly prototype: Intl.DateTimeFormat; }
+>Intl.DateTimeFormat : Intl.DateTimeFormatConstructor
 >Intl : typeof Intl
->DateTimeFormat : { (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; new (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; supportedLocalesOf(locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; readonly prototype: Intl.DateTimeFormat; }
+>DateTimeFormat : Intl.DateTimeFormatConstructor
 >formatRangeToParts : (startDate: number | bigint | Date, endDate: number | bigint | Date) => Intl.DateTimeRangeFormatPart[]
 
diff --git a/tests/baselines/reference/bigintWithLib.types b/tests/baselines/reference/bigintWithLib.types
index 659ef454134f8..52f029d8cd577 100644
--- a/tests/baselines/reference/bigintWithLib.types
+++ b/tests/baselines/reference/bigintWithLib.types
@@ -392,9 +392,9 @@ new Intl.NumberFormat("fr").format(3000n);
 >new Intl.NumberFormat("fr").format(3000n) : string
 >new Intl.NumberFormat("fr").format : { (value: number): string; (value: number | bigint): string; }
 >new Intl.NumberFormat("fr") : Intl.NumberFormat
->Intl.NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>Intl.NumberFormat : Intl.NumberFormatConstructor
 >Intl : typeof Intl
->NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>NumberFormat : Intl.NumberFormatConstructor
 >"fr" : "fr"
 >format : { (value: number): string; (value: number | bigint): string; }
 >3000n : 3000n
@@ -403,9 +403,9 @@ new Intl.NumberFormat("fr").format(bigintVal);
 >new Intl.NumberFormat("fr").format(bigintVal) : string
 >new Intl.NumberFormat("fr").format : { (value: number): string; (value: number | bigint): string; }
 >new Intl.NumberFormat("fr") : Intl.NumberFormat
->Intl.NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>Intl.NumberFormat : Intl.NumberFormatConstructor
 >Intl : typeof Intl
->NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>NumberFormat : Intl.NumberFormatConstructor
 >"fr" : "fr"
 >format : { (value: number): string; (value: number | bigint): string; }
 >bigintVal : bigint
diff --git a/tests/baselines/reference/bigintWithoutLib.types b/tests/baselines/reference/bigintWithoutLib.types
index 8935093c1338b..6789435ca906c 100644
--- a/tests/baselines/reference/bigintWithoutLib.types
+++ b/tests/baselines/reference/bigintWithoutLib.types
@@ -376,9 +376,9 @@ new Intl.NumberFormat("fr").format(3000n);
 >new Intl.NumberFormat("fr").format(3000n) : string
 >new Intl.NumberFormat("fr").format : (value: number) => string
 >new Intl.NumberFormat("fr") : Intl.NumberFormat
->Intl.NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>Intl.NumberFormat : Intl.NumberFormatConstructor
 >Intl : typeof Intl
->NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>NumberFormat : Intl.NumberFormatConstructor
 >"fr" : "fr"
 >format : (value: number) => string
 >3000n : 3000n
@@ -387,9 +387,9 @@ new Intl.NumberFormat("fr").format(bigintVal);
 >new Intl.NumberFormat("fr").format(bigintVal) : string
 >new Intl.NumberFormat("fr").format : (value: number) => string
 >new Intl.NumberFormat("fr") : Intl.NumberFormat
->Intl.NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>Intl.NumberFormat : Intl.NumberFormatConstructor
 >Intl : typeof Intl
->NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>NumberFormat : Intl.NumberFormatConstructor
 >"fr" : "fr"
 >format : (value: number) => string
 >bigintVal : bigint
diff --git a/tests/baselines/reference/doYouNeedToChangeYourTargetLibraryES2016Plus.types b/tests/baselines/reference/doYouNeedToChangeYourTargetLibraryES2016Plus.types
index ef5b52309ec8e..c24c8846bc11e 100644
--- a/tests/baselines/reference/doYouNeedToChangeYourTargetLibraryES2016Plus.types
+++ b/tests/baselines/reference/doYouNeedToChangeYourTargetLibraryES2016Plus.types
@@ -57,9 +57,9 @@ const testIntlFormatToParts = new Intl.DateTimeFormat("en-US").formatToParts();
 >new Intl.DateTimeFormat("en-US").formatToParts() : any
 >new Intl.DateTimeFormat("en-US").formatToParts : any
 >new Intl.DateTimeFormat("en-US") : Intl.DateTimeFormat
->Intl.DateTimeFormat : { (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; new (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; supportedLocalesOf(locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; readonly prototype: Intl.DateTimeFormat; }
+>Intl.DateTimeFormat : Intl.DateTimeFormatConstructor
 >Intl : typeof Intl
->DateTimeFormat : { (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; new (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; supportedLocalesOf(locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; readonly prototype: Intl.DateTimeFormat; }
+>DateTimeFormat : Intl.DateTimeFormatConstructor
 >"en-US" : "en-US"
 >formatToParts : any
 
@@ -150,9 +150,9 @@ const testNumberFormatFormatToParts = new Intl.NumberFormat("en-US").formatToPar
 >new Intl.NumberFormat("en-US").formatToParts() : any
 >new Intl.NumberFormat("en-US").formatToParts : any
 >new Intl.NumberFormat("en-US") : Intl.NumberFormat
->Intl.NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>Intl.NumberFormat : Intl.NumberFormatConstructor
 >Intl : typeof Intl
->NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>NumberFormat : Intl.NumberFormatConstructor
 >"en-US" : "en-US"
 >formatToParts : any
 
diff --git a/tests/baselines/reference/es2018IntlAPIs.symbols b/tests/baselines/reference/es2018IntlAPIs.symbols
index c76cf73671b18..56fe5b94adbb3 100644
--- a/tests/baselines/reference/es2018IntlAPIs.symbols
+++ b/tests/baselines/reference/es2018IntlAPIs.symbols
@@ -16,11 +16,11 @@ console.log(Intl.PluralRules.supportedLocalesOf(locales, options).join(', '));
 >console : Symbol(console, Decl(lib.dom.d.ts, --, --))
 >log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
 >Intl.PluralRules.supportedLocalesOf(locales, options).join : Symbol(Array.join, Decl(lib.es5.d.ts, --, --))
->Intl.PluralRules.supportedLocalesOf : Symbol(supportedLocalesOf, Decl(lib.es2018.intl.d.ts, --, --))
+>Intl.PluralRules.supportedLocalesOf : Symbol(Intl.PluralRulesConstructor.supportedLocalesOf, Decl(lib.es2018.intl.d.ts, --, --))
 >Intl.PluralRules : Symbol(Intl.PluralRules, Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --))
 >Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --))
 >PluralRules : Symbol(Intl.PluralRules, Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --))
->supportedLocalesOf : Symbol(supportedLocalesOf, Decl(lib.es2018.intl.d.ts, --, --))
+>supportedLocalesOf : Symbol(Intl.PluralRulesConstructor.supportedLocalesOf, Decl(lib.es2018.intl.d.ts, --, --))
 >locales : Symbol(locales, Decl(es2018IntlAPIs.ts, 2, 5))
 >options : Symbol(options, Decl(es2018IntlAPIs.ts, 3, 5))
 >join : Symbol(Array.join, Decl(lib.es5.d.ts, --, --))
diff --git a/tests/baselines/reference/es2018IntlAPIs.types b/tests/baselines/reference/es2018IntlAPIs.types
index 1de5c1cc79a25..b9631962c97d5 100644
--- a/tests/baselines/reference/es2018IntlAPIs.types
+++ b/tests/baselines/reference/es2018IntlAPIs.types
@@ -26,9 +26,9 @@ console.log(Intl.PluralRules.supportedLocalesOf(locales, options).join(', '));
 >Intl.PluralRules.supportedLocalesOf(locales, options).join : (separator?: string) => string
 >Intl.PluralRules.supportedLocalesOf(locales, options) : string[]
 >Intl.PluralRules.supportedLocalesOf : (locales: string | string[], options?: { localeMatcher?: "lookup" | "best fit"; }) => string[]
->Intl.PluralRules : { (locales?: string | string[], options?: Intl.PluralRulesOptions): Intl.PluralRules; new (locales?: string | string[], options?: Intl.PluralRulesOptions): Intl.PluralRules; supportedLocalesOf(locales: string | string[], options?: { localeMatcher?: "lookup" | "best fit"; }): string[]; }
+>Intl.PluralRules : Intl.PluralRulesConstructor
 >Intl : typeof Intl
->PluralRules : { (locales?: string | string[], options?: Intl.PluralRulesOptions): Intl.PluralRules; new (locales?: string | string[], options?: Intl.PluralRulesOptions): Intl.PluralRules; supportedLocalesOf(locales: string | string[], options?: { localeMatcher?: "lookup" | "best fit"; }): string[]; }
+>PluralRules : Intl.PluralRulesConstructor
 >supportedLocalesOf : (locales: string | string[], options?: { localeMatcher?: "lookup" | "best fit"; }) => string[]
 >locales : string[]
 >options : { readonly localeMatcher: "lookup"; }
diff --git a/tests/baselines/reference/es2020IntlAPIs.types b/tests/baselines/reference/es2020IntlAPIs.types
index 598446d7edaae..686d7e1d13777 100644
--- a/tests/baselines/reference/es2020IntlAPIs.types
+++ b/tests/baselines/reference/es2020IntlAPIs.types
@@ -27,18 +27,18 @@ function log(locale: string) {
 >new Intl.DateTimeFormat(locale).format(date) : string
 >new Intl.DateTimeFormat(locale).format : (date?: number | Date) => string
 >new Intl.DateTimeFormat(locale) : Intl.DateTimeFormat
->Intl.DateTimeFormat : { (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; new (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; supportedLocalesOf(locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; readonly prototype: Intl.DateTimeFormat; }
+>Intl.DateTimeFormat : Intl.DateTimeFormatConstructor
 >Intl : typeof Intl
->DateTimeFormat : { (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; new (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; supportedLocalesOf(locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; readonly prototype: Intl.DateTimeFormat; }
+>DateTimeFormat : Intl.DateTimeFormatConstructor
 >locale : string
 >format : (date?: number | Date) => string
 >date : Date
 >new Intl.NumberFormat(locale).format(count) : string
 >new Intl.NumberFormat(locale).format : { (value: number): string; (value: number | bigint): string; }
 >new Intl.NumberFormat(locale) : Intl.NumberFormat
->Intl.NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>Intl.NumberFormat : Intl.NumberFormatConstructor
 >Intl : typeof Intl
->NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>NumberFormat : Intl.NumberFormatConstructor
 >locale : string
 >format : { (value: number): string; (value: number | bigint): string; }
 >count : 26254.39
@@ -64,9 +64,9 @@ log("de-DE");
 const rtf1 = new Intl.RelativeTimeFormat('en', { style: 'narrow' });
 >rtf1 : Intl.RelativeTimeFormat
 >new Intl.RelativeTimeFormat('en', { style: 'narrow' }) : Intl.RelativeTimeFormat
->Intl.RelativeTimeFormat : { new (locales?: string | string[], options?: Intl.RelativeTimeFormatOptions): Intl.RelativeTimeFormat; supportedLocalesOf(locales?: string | string[], options?: Intl.RelativeTimeFormatOptions): string[]; }
+>Intl.RelativeTimeFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): Intl.RelativeTimeFormat; supportedLocalesOf(locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): string[]; }
 >Intl : typeof Intl
->RelativeTimeFormat : { new (locales?: string | string[], options?: Intl.RelativeTimeFormatOptions): Intl.RelativeTimeFormat; supportedLocalesOf(locales?: string | string[], options?: Intl.RelativeTimeFormatOptions): string[]; }
+>RelativeTimeFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): Intl.RelativeTimeFormat; supportedLocalesOf(locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): string[]; }
 >'en' : "en"
 >{ style: 'narrow' } : { style: "narrow"; }
 >style : "narrow"
@@ -104,9 +104,9 @@ console.log(rtf1.format(-1, 'day'));
 const rtf2 = new Intl.RelativeTimeFormat('es', { numeric: 'auto' });
 >rtf2 : Intl.RelativeTimeFormat
 >new Intl.RelativeTimeFormat('es', { numeric: 'auto' }) : Intl.RelativeTimeFormat
->Intl.RelativeTimeFormat : { new (locales?: string | string[], options?: Intl.RelativeTimeFormatOptions): Intl.RelativeTimeFormat; supportedLocalesOf(locales?: string | string[], options?: Intl.RelativeTimeFormatOptions): string[]; }
+>Intl.RelativeTimeFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): Intl.RelativeTimeFormat; supportedLocalesOf(locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): string[]; }
 >Intl : typeof Intl
->RelativeTimeFormat : { new (locales?: string | string[], options?: Intl.RelativeTimeFormatOptions): Intl.RelativeTimeFormat; supportedLocalesOf(locales?: string | string[], options?: Intl.RelativeTimeFormatOptions): string[]; }
+>RelativeTimeFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): Intl.RelativeTimeFormat; supportedLocalesOf(locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): string[]; }
 >'es' : "es"
 >{ numeric: 'auto' } : { numeric: "auto"; }
 >numeric : "auto"
diff --git a/tests/baselines/reference/es2021LocalesObjectArgument.js b/tests/baselines/reference/es2021LocalesObjectArgument.js
new file mode 100644
index 0000000000000..4287c3f534793
--- /dev/null
+++ b/tests/baselines/reference/es2021LocalesObjectArgument.js
@@ -0,0 +1,21 @@
+//// [tests/cases/conformance/es2021/es2021LocalesObjectArgument.ts] ////
+
+//// [es2021LocalesObjectArgument.ts]
+const enUS = new Intl.Locale("en-US");
+const deDE = new Intl.Locale("de-DE");
+const jaJP = new Intl.Locale("ja-JP");
+
+new Intl.ListFormat(enUS);
+new Intl.ListFormat([deDE, jaJP]);
+Intl.ListFormat.supportedLocalesOf(enUS);
+Intl.ListFormat.supportedLocalesOf([deDE, jaJP]);
+
+
+//// [es2021LocalesObjectArgument.js]
+const enUS = new Intl.Locale("en-US");
+const deDE = new Intl.Locale("de-DE");
+const jaJP = new Intl.Locale("ja-JP");
+new Intl.ListFormat(enUS);
+new Intl.ListFormat([deDE, jaJP]);
+Intl.ListFormat.supportedLocalesOf(enUS);
+Intl.ListFormat.supportedLocalesOf([deDE, jaJP]);
diff --git a/tests/baselines/reference/es2021LocalesObjectArgument.symbols b/tests/baselines/reference/es2021LocalesObjectArgument.symbols
new file mode 100644
index 0000000000000..877746c916e94
--- /dev/null
+++ b/tests/baselines/reference/es2021LocalesObjectArgument.symbols
@@ -0,0 +1,51 @@
+//// [tests/cases/conformance/es2021/es2021LocalesObjectArgument.ts] ////
+
+=== es2021LocalesObjectArgument.ts ===
+const enUS = new Intl.Locale("en-US");
+>enUS : Symbol(enUS, Decl(es2021LocalesObjectArgument.ts, 0, 5))
+>Intl.Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 3 more)
+>Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+
+const deDE = new Intl.Locale("de-DE");
+>deDE : Symbol(deDE, Decl(es2021LocalesObjectArgument.ts, 1, 5))
+>Intl.Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 3 more)
+>Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+
+const jaJP = new Intl.Locale("ja-JP");
+>jaJP : Symbol(jaJP, Decl(es2021LocalesObjectArgument.ts, 2, 5))
+>Intl.Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 3 more)
+>Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+
+new Intl.ListFormat(enUS);
+>Intl.ListFormat : Symbol(Intl.ListFormat, Decl(lib.es2021.intl.d.ts, --, --), Decl(lib.es2021.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 3 more)
+>ListFormat : Symbol(Intl.ListFormat, Decl(lib.es2021.intl.d.ts, --, --), Decl(lib.es2021.intl.d.ts, --, --))
+>enUS : Symbol(enUS, Decl(es2021LocalesObjectArgument.ts, 0, 5))
+
+new Intl.ListFormat([deDE, jaJP]);
+>Intl.ListFormat : Symbol(Intl.ListFormat, Decl(lib.es2021.intl.d.ts, --, --), Decl(lib.es2021.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 3 more)
+>ListFormat : Symbol(Intl.ListFormat, Decl(lib.es2021.intl.d.ts, --, --), Decl(lib.es2021.intl.d.ts, --, --))
+>deDE : Symbol(deDE, Decl(es2021LocalesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(es2021LocalesObjectArgument.ts, 2, 5))
+
+Intl.ListFormat.supportedLocalesOf(enUS);
+>Intl.ListFormat.supportedLocalesOf : Symbol(supportedLocalesOf, Decl(lib.es2021.intl.d.ts, --, --))
+>Intl.ListFormat : Symbol(Intl.ListFormat, Decl(lib.es2021.intl.d.ts, --, --), Decl(lib.es2021.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 3 more)
+>ListFormat : Symbol(Intl.ListFormat, Decl(lib.es2021.intl.d.ts, --, --), Decl(lib.es2021.intl.d.ts, --, --))
+>supportedLocalesOf : Symbol(supportedLocalesOf, Decl(lib.es2021.intl.d.ts, --, --))
+>enUS : Symbol(enUS, Decl(es2021LocalesObjectArgument.ts, 0, 5))
+
+Intl.ListFormat.supportedLocalesOf([deDE, jaJP]);
+>Intl.ListFormat.supportedLocalesOf : Symbol(supportedLocalesOf, Decl(lib.es2021.intl.d.ts, --, --))
+>Intl.ListFormat : Symbol(Intl.ListFormat, Decl(lib.es2021.intl.d.ts, --, --), Decl(lib.es2021.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 3 more)
+>ListFormat : Symbol(Intl.ListFormat, Decl(lib.es2021.intl.d.ts, --, --), Decl(lib.es2021.intl.d.ts, --, --))
+>supportedLocalesOf : Symbol(supportedLocalesOf, Decl(lib.es2021.intl.d.ts, --, --))
+>deDE : Symbol(deDE, Decl(es2021LocalesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(es2021LocalesObjectArgument.ts, 2, 5))
+
diff --git a/tests/baselines/reference/es2021LocalesObjectArgument.types b/tests/baselines/reference/es2021LocalesObjectArgument.types
new file mode 100644
index 0000000000000..85014f03fc5e6
--- /dev/null
+++ b/tests/baselines/reference/es2021LocalesObjectArgument.types
@@ -0,0 +1,63 @@
+//// [tests/cases/conformance/es2021/es2021LocalesObjectArgument.ts] ////
+
+=== es2021LocalesObjectArgument.ts ===
+const enUS = new Intl.Locale("en-US");
+>enUS : Intl.Locale
+>new Intl.Locale("en-US") : Intl.Locale
+>Intl.Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>Intl : typeof Intl
+>Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>"en-US" : "en-US"
+
+const deDE = new Intl.Locale("de-DE");
+>deDE : Intl.Locale
+>new Intl.Locale("de-DE") : Intl.Locale
+>Intl.Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>Intl : typeof Intl
+>Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>"de-DE" : "de-DE"
+
+const jaJP = new Intl.Locale("ja-JP");
+>jaJP : Intl.Locale
+>new Intl.Locale("ja-JP") : Intl.Locale
+>Intl.Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>Intl : typeof Intl
+>Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>"ja-JP" : "ja-JP"
+
+new Intl.ListFormat(enUS);
+>new Intl.ListFormat(enUS) : Intl.ListFormat
+>Intl.ListFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.ListFormatOptions): Intl.ListFormat; prototype: Intl.ListFormat; supportedLocalesOf(locales: Intl.LocalesArgument, options?: Pick<Intl.ListFormatOptions, "localeMatcher">): string[]; }
+>Intl : typeof Intl
+>ListFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.ListFormatOptions): Intl.ListFormat; prototype: Intl.ListFormat; supportedLocalesOf(locales: Intl.LocalesArgument, options?: Pick<Intl.ListFormatOptions, "localeMatcher">): string[]; }
+>enUS : Intl.Locale
+
+new Intl.ListFormat([deDE, jaJP]);
+>new Intl.ListFormat([deDE, jaJP]) : Intl.ListFormat
+>Intl.ListFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.ListFormatOptions): Intl.ListFormat; prototype: Intl.ListFormat; supportedLocalesOf(locales: Intl.LocalesArgument, options?: Pick<Intl.ListFormatOptions, "localeMatcher">): string[]; }
+>Intl : typeof Intl
+>ListFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.ListFormatOptions): Intl.ListFormat; prototype: Intl.ListFormat; supportedLocalesOf(locales: Intl.LocalesArgument, options?: Pick<Intl.ListFormatOptions, "localeMatcher">): string[]; }
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
+Intl.ListFormat.supportedLocalesOf(enUS);
+>Intl.ListFormat.supportedLocalesOf(enUS) : string[]
+>Intl.ListFormat.supportedLocalesOf : (locales: Intl.LocalesArgument, options?: Pick<Intl.ListFormatOptions, "localeMatcher">) => string[]
+>Intl.ListFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.ListFormatOptions): Intl.ListFormat; prototype: Intl.ListFormat; supportedLocalesOf(locales: Intl.LocalesArgument, options?: Pick<Intl.ListFormatOptions, "localeMatcher">): string[]; }
+>Intl : typeof Intl
+>ListFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.ListFormatOptions): Intl.ListFormat; prototype: Intl.ListFormat; supportedLocalesOf(locales: Intl.LocalesArgument, options?: Pick<Intl.ListFormatOptions, "localeMatcher">): string[]; }
+>supportedLocalesOf : (locales: Intl.LocalesArgument, options?: Pick<Intl.ListFormatOptions, "localeMatcher">) => string[]
+>enUS : Intl.Locale
+
+Intl.ListFormat.supportedLocalesOf([deDE, jaJP]);
+>Intl.ListFormat.supportedLocalesOf([deDE, jaJP]) : string[]
+>Intl.ListFormat.supportedLocalesOf : (locales: Intl.LocalesArgument, options?: Pick<Intl.ListFormatOptions, "localeMatcher">) => string[]
+>Intl.ListFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.ListFormatOptions): Intl.ListFormat; prototype: Intl.ListFormat; supportedLocalesOf(locales: Intl.LocalesArgument, options?: Pick<Intl.ListFormatOptions, "localeMatcher">): string[]; }
+>Intl : typeof Intl
+>ListFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.ListFormatOptions): Intl.ListFormat; prototype: Intl.ListFormat; supportedLocalesOf(locales: Intl.LocalesArgument, options?: Pick<Intl.ListFormatOptions, "localeMatcher">): string[]; }
+>supportedLocalesOf : (locales: Intl.LocalesArgument, options?: Pick<Intl.ListFormatOptions, "localeMatcher">) => string[]
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
diff --git a/tests/baselines/reference/es2022IntlAPIs.types b/tests/baselines/reference/es2022IntlAPIs.types
index 74d524e218fba..ac0c770abeb85 100644
--- a/tests/baselines/reference/es2022IntlAPIs.types
+++ b/tests/baselines/reference/es2022IntlAPIs.types
@@ -20,9 +20,9 @@ for (const zoneName of timezoneNames) {
   var formatter = new Intl.DateTimeFormat('en-US', {
 >formatter : Intl.DateTimeFormat
 >new Intl.DateTimeFormat('en-US', {    timeZone: 'America/Los_Angeles',    timeZoneName: zoneName,  }) : Intl.DateTimeFormat
->Intl.DateTimeFormat : { (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; new (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; supportedLocalesOf(locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; readonly prototype: Intl.DateTimeFormat; }
+>Intl.DateTimeFormat : Intl.DateTimeFormatConstructor
 >Intl : typeof Intl
->DateTimeFormat : { (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; new (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; supportedLocalesOf(locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; readonly prototype: Intl.DateTimeFormat; }
+>DateTimeFormat : Intl.DateTimeFormatConstructor
 >'en-US' : "en-US"
 >{    timeZone: 'America/Los_Angeles',    timeZoneName: zoneName,  } : { timeZone: string; timeZoneName: "short" | "long" | "shortOffset" | "longOffset" | "shortGeneric" | "longGeneric"; }
 
diff --git a/tests/baselines/reference/es2022LocalesObjectArgument.js b/tests/baselines/reference/es2022LocalesObjectArgument.js
new file mode 100644
index 0000000000000..335b921f8222a
--- /dev/null
+++ b/tests/baselines/reference/es2022LocalesObjectArgument.js
@@ -0,0 +1,21 @@
+//// [tests/cases/conformance/es2022/es2022LocalesObjectArgument.ts] ////
+
+//// [es2022LocalesObjectArgument.ts]
+const enUS = new Intl.Locale("en-US");
+const deDE = new Intl.Locale("de-DE");
+const jaJP = new Intl.Locale("ja-JP");
+
+new Intl.Segmenter(enUS);
+new Intl.Segmenter([deDE, jaJP]);
+Intl.Segmenter.supportedLocalesOf(enUS);
+Intl.Segmenter.supportedLocalesOf([deDE, jaJP]);
+
+
+//// [es2022LocalesObjectArgument.js]
+const enUS = new Intl.Locale("en-US");
+const deDE = new Intl.Locale("de-DE");
+const jaJP = new Intl.Locale("ja-JP");
+new Intl.Segmenter(enUS);
+new Intl.Segmenter([deDE, jaJP]);
+Intl.Segmenter.supportedLocalesOf(enUS);
+Intl.Segmenter.supportedLocalesOf([deDE, jaJP]);
diff --git a/tests/baselines/reference/es2022LocalesObjectArgument.symbols b/tests/baselines/reference/es2022LocalesObjectArgument.symbols
new file mode 100644
index 0000000000000..41adb92a2aee8
--- /dev/null
+++ b/tests/baselines/reference/es2022LocalesObjectArgument.symbols
@@ -0,0 +1,51 @@
+//// [tests/cases/conformance/es2022/es2022LocalesObjectArgument.ts] ////
+
+=== es2022LocalesObjectArgument.ts ===
+const enUS = new Intl.Locale("en-US");
+>enUS : Symbol(enUS, Decl(es2022LocalesObjectArgument.ts, 0, 5))
+>Intl.Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 4 more)
+>Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+
+const deDE = new Intl.Locale("de-DE");
+>deDE : Symbol(deDE, Decl(es2022LocalesObjectArgument.ts, 1, 5))
+>Intl.Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 4 more)
+>Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+
+const jaJP = new Intl.Locale("ja-JP");
+>jaJP : Symbol(jaJP, Decl(es2022LocalesObjectArgument.ts, 2, 5))
+>Intl.Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 4 more)
+>Locale : Symbol(Intl.Locale, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+
+new Intl.Segmenter(enUS);
+>Intl.Segmenter : Symbol(Intl.Segmenter, Decl(lib.es2022.intl.d.ts, --, --), Decl(lib.es2022.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 4 more)
+>Segmenter : Symbol(Intl.Segmenter, Decl(lib.es2022.intl.d.ts, --, --), Decl(lib.es2022.intl.d.ts, --, --))
+>enUS : Symbol(enUS, Decl(es2022LocalesObjectArgument.ts, 0, 5))
+
+new Intl.Segmenter([deDE, jaJP]);
+>Intl.Segmenter : Symbol(Intl.Segmenter, Decl(lib.es2022.intl.d.ts, --, --), Decl(lib.es2022.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 4 more)
+>Segmenter : Symbol(Intl.Segmenter, Decl(lib.es2022.intl.d.ts, --, --), Decl(lib.es2022.intl.d.ts, --, --))
+>deDE : Symbol(deDE, Decl(es2022LocalesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(es2022LocalesObjectArgument.ts, 2, 5))
+
+Intl.Segmenter.supportedLocalesOf(enUS);
+>Intl.Segmenter.supportedLocalesOf : Symbol(supportedLocalesOf, Decl(lib.es2022.intl.d.ts, --, --))
+>Intl.Segmenter : Symbol(Intl.Segmenter, Decl(lib.es2022.intl.d.ts, --, --), Decl(lib.es2022.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 4 more)
+>Segmenter : Symbol(Intl.Segmenter, Decl(lib.es2022.intl.d.ts, --, --), Decl(lib.es2022.intl.d.ts, --, --))
+>supportedLocalesOf : Symbol(supportedLocalesOf, Decl(lib.es2022.intl.d.ts, --, --))
+>enUS : Symbol(enUS, Decl(es2022LocalesObjectArgument.ts, 0, 5))
+
+Intl.Segmenter.supportedLocalesOf([deDE, jaJP]);
+>Intl.Segmenter.supportedLocalesOf : Symbol(supportedLocalesOf, Decl(lib.es2022.intl.d.ts, --, --))
+>Intl.Segmenter : Symbol(Intl.Segmenter, Decl(lib.es2022.intl.d.ts, --, --), Decl(lib.es2022.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 4 more)
+>Segmenter : Symbol(Intl.Segmenter, Decl(lib.es2022.intl.d.ts, --, --), Decl(lib.es2022.intl.d.ts, --, --))
+>supportedLocalesOf : Symbol(supportedLocalesOf, Decl(lib.es2022.intl.d.ts, --, --))
+>deDE : Symbol(deDE, Decl(es2022LocalesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(es2022LocalesObjectArgument.ts, 2, 5))
+
diff --git a/tests/baselines/reference/es2022LocalesObjectArgument.types b/tests/baselines/reference/es2022LocalesObjectArgument.types
new file mode 100644
index 0000000000000..caf2b02231698
--- /dev/null
+++ b/tests/baselines/reference/es2022LocalesObjectArgument.types
@@ -0,0 +1,63 @@
+//// [tests/cases/conformance/es2022/es2022LocalesObjectArgument.ts] ////
+
+=== es2022LocalesObjectArgument.ts ===
+const enUS = new Intl.Locale("en-US");
+>enUS : Intl.Locale
+>new Intl.Locale("en-US") : Intl.Locale
+>Intl.Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>Intl : typeof Intl
+>Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>"en-US" : "en-US"
+
+const deDE = new Intl.Locale("de-DE");
+>deDE : Intl.Locale
+>new Intl.Locale("de-DE") : Intl.Locale
+>Intl.Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>Intl : typeof Intl
+>Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>"de-DE" : "de-DE"
+
+const jaJP = new Intl.Locale("ja-JP");
+>jaJP : Intl.Locale
+>new Intl.Locale("ja-JP") : Intl.Locale
+>Intl.Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>Intl : typeof Intl
+>Locale : new (tag: string | Intl.Locale, options?: Intl.LocaleOptions) => Intl.Locale
+>"ja-JP" : "ja-JP"
+
+new Intl.Segmenter(enUS);
+>new Intl.Segmenter(enUS) : Intl.Segmenter
+>Intl.Segmenter : { new (locales?: Intl.LocalesArgument, options?: Intl.SegmenterOptions): Intl.Segmenter; prototype: Intl.Segmenter; supportedLocalesOf(locales: Intl.LocalesArgument, options?: Pick<Intl.SegmenterOptions, "localeMatcher">): string[]; }
+>Intl : typeof Intl
+>Segmenter : { new (locales?: Intl.LocalesArgument, options?: Intl.SegmenterOptions): Intl.Segmenter; prototype: Intl.Segmenter; supportedLocalesOf(locales: Intl.LocalesArgument, options?: Pick<Intl.SegmenterOptions, "localeMatcher">): string[]; }
+>enUS : Intl.Locale
+
+new Intl.Segmenter([deDE, jaJP]);
+>new Intl.Segmenter([deDE, jaJP]) : Intl.Segmenter
+>Intl.Segmenter : { new (locales?: Intl.LocalesArgument, options?: Intl.SegmenterOptions): Intl.Segmenter; prototype: Intl.Segmenter; supportedLocalesOf(locales: Intl.LocalesArgument, options?: Pick<Intl.SegmenterOptions, "localeMatcher">): string[]; }
+>Intl : typeof Intl
+>Segmenter : { new (locales?: Intl.LocalesArgument, options?: Intl.SegmenterOptions): Intl.Segmenter; prototype: Intl.Segmenter; supportedLocalesOf(locales: Intl.LocalesArgument, options?: Pick<Intl.SegmenterOptions, "localeMatcher">): string[]; }
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
+Intl.Segmenter.supportedLocalesOf(enUS);
+>Intl.Segmenter.supportedLocalesOf(enUS) : string[]
+>Intl.Segmenter.supportedLocalesOf : (locales: Intl.LocalesArgument, options?: Pick<Intl.SegmenterOptions, "localeMatcher">) => string[]
+>Intl.Segmenter : { new (locales?: Intl.LocalesArgument, options?: Intl.SegmenterOptions): Intl.Segmenter; prototype: Intl.Segmenter; supportedLocalesOf(locales: Intl.LocalesArgument, options?: Pick<Intl.SegmenterOptions, "localeMatcher">): string[]; }
+>Intl : typeof Intl
+>Segmenter : { new (locales?: Intl.LocalesArgument, options?: Intl.SegmenterOptions): Intl.Segmenter; prototype: Intl.Segmenter; supportedLocalesOf(locales: Intl.LocalesArgument, options?: Pick<Intl.SegmenterOptions, "localeMatcher">): string[]; }
+>supportedLocalesOf : (locales: Intl.LocalesArgument, options?: Pick<Intl.SegmenterOptions, "localeMatcher">) => string[]
+>enUS : Intl.Locale
+
+Intl.Segmenter.supportedLocalesOf([deDE, jaJP]);
+>Intl.Segmenter.supportedLocalesOf([deDE, jaJP]) : string[]
+>Intl.Segmenter.supportedLocalesOf : (locales: Intl.LocalesArgument, options?: Pick<Intl.SegmenterOptions, "localeMatcher">) => string[]
+>Intl.Segmenter : { new (locales?: Intl.LocalesArgument, options?: Intl.SegmenterOptions): Intl.Segmenter; prototype: Intl.Segmenter; supportedLocalesOf(locales: Intl.LocalesArgument, options?: Pick<Intl.SegmenterOptions, "localeMatcher">): string[]; }
+>Intl : typeof Intl
+>Segmenter : { new (locales?: Intl.LocalesArgument, options?: Intl.SegmenterOptions): Intl.Segmenter; prototype: Intl.Segmenter; supportedLocalesOf(locales: Intl.LocalesArgument, options?: Pick<Intl.SegmenterOptions, "localeMatcher">): string[]; }
+>supportedLocalesOf : (locales: Intl.LocalesArgument, options?: Pick<Intl.SegmenterOptions, "localeMatcher">) => string[]
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
diff --git a/tests/baselines/reference/formatToPartsBigInt.types b/tests/baselines/reference/formatToPartsBigInt.types
index 57a175802cc2a..3b42619f102e0 100644
--- a/tests/baselines/reference/formatToPartsBigInt.types
+++ b/tests/baselines/reference/formatToPartsBigInt.types
@@ -8,9 +8,9 @@ new Intl.NumberFormat("fr").formatToParts(3000n);
 >new Intl.NumberFormat("fr").formatToParts(3000n) : Intl.NumberFormatPart[]
 >new Intl.NumberFormat("fr").formatToParts : (number?: number | bigint) => Intl.NumberFormatPart[]
 >new Intl.NumberFormat("fr") : Intl.NumberFormat
->Intl.NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>Intl.NumberFormat : Intl.NumberFormatConstructor
 >Intl : typeof Intl
->NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>NumberFormat : Intl.NumberFormatConstructor
 >"fr" : "fr"
 >formatToParts : (number?: number | bigint) => Intl.NumberFormatPart[]
 >3000n : 3000n
@@ -19,9 +19,9 @@ new Intl.NumberFormat("fr").formatToParts(BigInt(123));
 >new Intl.NumberFormat("fr").formatToParts(BigInt(123)) : Intl.NumberFormatPart[]
 >new Intl.NumberFormat("fr").formatToParts : (number?: number | bigint) => Intl.NumberFormatPart[]
 >new Intl.NumberFormat("fr") : Intl.NumberFormat
->Intl.NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>Intl.NumberFormat : Intl.NumberFormatConstructor
 >Intl : typeof Intl
->NumberFormat : { (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; new (locales?: string | string[], options?: Intl.NumberFormatOptions): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions): string[]; readonly prototype: Intl.NumberFormat; }
+>NumberFormat : Intl.NumberFormatConstructor
 >"fr" : "fr"
 >formatToParts : (number?: number | bigint) => Intl.NumberFormatPart[]
 >BigInt(123) : bigint
diff --git a/tests/baselines/reference/formatToPartsFractionalSecond.types b/tests/baselines/reference/formatToPartsFractionalSecond.types
index 952d5c5144798..f25c5d22c9124 100644
--- a/tests/baselines/reference/formatToPartsFractionalSecond.types
+++ b/tests/baselines/reference/formatToPartsFractionalSecond.types
@@ -7,9 +7,9 @@ new Intl.DateTimeFormat().formatToParts().find((val) => val.type === 'fractional
 >new Intl.DateTimeFormat().formatToParts() : Intl.DateTimeFormatPart[]
 >new Intl.DateTimeFormat().formatToParts : (date?: number | Date) => Intl.DateTimeFormatPart[]
 >new Intl.DateTimeFormat() : Intl.DateTimeFormat
->Intl.DateTimeFormat : { (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; new (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; supportedLocalesOf(locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; readonly prototype: Intl.DateTimeFormat; }
+>Intl.DateTimeFormat : Intl.DateTimeFormatConstructor
 >Intl : typeof Intl
->DateTimeFormat : { (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; new (locales?: string | string[], options?: Intl.DateTimeFormatOptions): Intl.DateTimeFormat; supportedLocalesOf(locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; readonly prototype: Intl.DateTimeFormat; }
+>DateTimeFormat : Intl.DateTimeFormatConstructor
 >formatToParts : (date?: number | Date) => Intl.DateTimeFormatPart[]
 >find : { <S extends Intl.DateTimeFormatPart>(predicate: (value: Intl.DateTimeFormatPart, index: number, obj: Intl.DateTimeFormatPart[]) => value is S, thisArg?: any): S; (predicate: (value: Intl.DateTimeFormatPart, index: number, obj: Intl.DateTimeFormatPart[]) => unknown, thisArg?: any): Intl.DateTimeFormatPart; }
 >(val) => val.type === 'fractionalSecond' : (val: Intl.DateTimeFormatPart) => boolean
diff --git a/tests/baselines/reference/localesObjectArgument.js b/tests/baselines/reference/localesObjectArgument.js
index 1136ea6364ebd..59a1ddaa9d370 100644
--- a/tests/baselines/reference/localesObjectArgument.js
+++ b/tests/baselines/reference/localesObjectArgument.js
@@ -8,6 +8,7 @@ const jaJP = new Intl.Locale("ja-JP");
 const now = new Date();
 const num = 1000;
 const bigint = 123456789123456789n;
+const str = "";
 
 now.toLocaleString(enUS);
 now.toLocaleDateString(enUS);
@@ -21,6 +22,38 @@ num.toLocaleString([deDE, jaJP]);
 
 bigint.toLocaleString(enUS);
 bigint.toLocaleString([deDE, jaJP]);
+
+str.toLocaleLowerCase(enUS);
+str.toLocaleLowerCase([deDE, jaJP]);
+str.toLocaleUpperCase(enUS);
+str.toLocaleUpperCase([deDE, jaJP]);
+str.localeCompare(str, enUS);
+str.localeCompare(str, [deDE, jaJP]);
+
+new Intl.PluralRules(enUS);
+new Intl.PluralRules([deDE, jaJP]);
+Intl.PluralRules.supportedLocalesOf(enUS);
+Intl.PluralRules.supportedLocalesOf([deDE, jaJP]);
+
+new Intl.RelativeTimeFormat(enUS);
+new Intl.RelativeTimeFormat([deDE, jaJP]);
+Intl.RelativeTimeFormat.supportedLocalesOf(enUS);
+Intl.RelativeTimeFormat.supportedLocalesOf([deDE, jaJP]);
+
+new Intl.Collator(enUS);
+new Intl.Collator([deDE, jaJP]);
+Intl.Collator.supportedLocalesOf(enUS);
+Intl.Collator.supportedLocalesOf([deDE, jaJP]);
+
+new Intl.DateTimeFormat(enUS);
+new Intl.DateTimeFormat([deDE, jaJP]);
+Intl.DateTimeFormat.supportedLocalesOf(enUS);
+Intl.DateTimeFormat.supportedLocalesOf([deDE, jaJP]);
+
+new Intl.NumberFormat(enUS);
+new Intl.NumberFormat([deDE, jaJP]);
+Intl.NumberFormat.supportedLocalesOf(enUS);
+Intl.NumberFormat.supportedLocalesOf([deDE, jaJP]);
 
 
 //// [localesObjectArgument.js]
@@ -30,6 +63,7 @@ const jaJP = new Intl.Locale("ja-JP");
 const now = new Date();
 const num = 1000;
 const bigint = 123456789123456789n;
+const str = "";
 now.toLocaleString(enUS);
 now.toLocaleDateString(enUS);
 now.toLocaleTimeString(enUS);
@@ -40,3 +74,29 @@ num.toLocaleString(enUS);
 num.toLocaleString([deDE, jaJP]);
 bigint.toLocaleString(enUS);
 bigint.toLocaleString([deDE, jaJP]);
+str.toLocaleLowerCase(enUS);
+str.toLocaleLowerCase([deDE, jaJP]);
+str.toLocaleUpperCase(enUS);
+str.toLocaleUpperCase([deDE, jaJP]);
+str.localeCompare(str, enUS);
+str.localeCompare(str, [deDE, jaJP]);
+new Intl.PluralRules(enUS);
+new Intl.PluralRules([deDE, jaJP]);
+Intl.PluralRules.supportedLocalesOf(enUS);
+Intl.PluralRules.supportedLocalesOf([deDE, jaJP]);
+new Intl.RelativeTimeFormat(enUS);
+new Intl.RelativeTimeFormat([deDE, jaJP]);
+Intl.RelativeTimeFormat.supportedLocalesOf(enUS);
+Intl.RelativeTimeFormat.supportedLocalesOf([deDE, jaJP]);
+new Intl.Collator(enUS);
+new Intl.Collator([deDE, jaJP]);
+Intl.Collator.supportedLocalesOf(enUS);
+Intl.Collator.supportedLocalesOf([deDE, jaJP]);
+new Intl.DateTimeFormat(enUS);
+new Intl.DateTimeFormat([deDE, jaJP]);
+Intl.DateTimeFormat.supportedLocalesOf(enUS);
+Intl.DateTimeFormat.supportedLocalesOf([deDE, jaJP]);
+new Intl.NumberFormat(enUS);
+new Intl.NumberFormat([deDE, jaJP]);
+Intl.NumberFormat.supportedLocalesOf(enUS);
+Intl.NumberFormat.supportedLocalesOf([deDE, jaJP]);
diff --git a/tests/baselines/reference/localesObjectArgument.symbols b/tests/baselines/reference/localesObjectArgument.symbols
index 7b8e692cadfd6..c2c21e668249e 100644
--- a/tests/baselines/reference/localesObjectArgument.symbols
+++ b/tests/baselines/reference/localesObjectArgument.symbols
@@ -29,6 +29,9 @@ const num = 1000;
 const bigint = 123456789123456789n;
 >bigint : Symbol(bigint, Decl(localesObjectArgument.ts, 6, 5))
 
+const str = "";
+>str : Symbol(str, Decl(localesObjectArgument.ts, 7, 5))
+
 now.toLocaleString(enUS);
 >now.toLocaleString : Symbol(Date.toLocaleString, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.date.d.ts, --, --))
 >now : Symbol(now, Decl(localesObjectArgument.ts, 4, 5))
@@ -94,3 +97,194 @@ bigint.toLocaleString([deDE, jaJP]);
 >deDE : Symbol(deDE, Decl(localesObjectArgument.ts, 1, 5))
 >jaJP : Symbol(jaJP, Decl(localesObjectArgument.ts, 2, 5))
 
+str.toLocaleLowerCase(enUS);
+>str.toLocaleLowerCase : Symbol(String.toLocaleLowerCase, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.string.d.ts, --, --))
+>str : Symbol(str, Decl(localesObjectArgument.ts, 7, 5))
+>toLocaleLowerCase : Symbol(String.toLocaleLowerCase, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.string.d.ts, --, --))
+>enUS : Symbol(enUS, Decl(localesObjectArgument.ts, 0, 5))
+
+str.toLocaleLowerCase([deDE, jaJP]);
+>str.toLocaleLowerCase : Symbol(String.toLocaleLowerCase, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.string.d.ts, --, --))
+>str : Symbol(str, Decl(localesObjectArgument.ts, 7, 5))
+>toLocaleLowerCase : Symbol(String.toLocaleLowerCase, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.string.d.ts, --, --))
+>deDE : Symbol(deDE, Decl(localesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(localesObjectArgument.ts, 2, 5))
+
+str.toLocaleUpperCase(enUS);
+>str.toLocaleUpperCase : Symbol(String.toLocaleUpperCase, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.string.d.ts, --, --))
+>str : Symbol(str, Decl(localesObjectArgument.ts, 7, 5))
+>toLocaleUpperCase : Symbol(String.toLocaleUpperCase, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.string.d.ts, --, --))
+>enUS : Symbol(enUS, Decl(localesObjectArgument.ts, 0, 5))
+
+str.toLocaleUpperCase([deDE, jaJP]);
+>str.toLocaleUpperCase : Symbol(String.toLocaleUpperCase, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.string.d.ts, --, --))
+>str : Symbol(str, Decl(localesObjectArgument.ts, 7, 5))
+>toLocaleUpperCase : Symbol(String.toLocaleUpperCase, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.string.d.ts, --, --))
+>deDE : Symbol(deDE, Decl(localesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(localesObjectArgument.ts, 2, 5))
+
+str.localeCompare(str, enUS);
+>str.localeCompare : Symbol(String.localeCompare, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.string.d.ts, --, --))
+>str : Symbol(str, Decl(localesObjectArgument.ts, 7, 5))
+>localeCompare : Symbol(String.localeCompare, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.string.d.ts, --, --))
+>str : Symbol(str, Decl(localesObjectArgument.ts, 7, 5))
+>enUS : Symbol(enUS, Decl(localesObjectArgument.ts, 0, 5))
+
+str.localeCompare(str, [deDE, jaJP]);
+>str.localeCompare : Symbol(String.localeCompare, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.string.d.ts, --, --))
+>str : Symbol(str, Decl(localesObjectArgument.ts, 7, 5))
+>localeCompare : Symbol(String.localeCompare, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.string.d.ts, --, --))
+>str : Symbol(str, Decl(localesObjectArgument.ts, 7, 5))
+>deDE : Symbol(deDE, Decl(localesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(localesObjectArgument.ts, 2, 5))
+
+new Intl.PluralRules(enUS);
+>Intl.PluralRules : Symbol(Intl.PluralRules, Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>PluralRules : Symbol(Intl.PluralRules, Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --))
+>enUS : Symbol(enUS, Decl(localesObjectArgument.ts, 0, 5))
+
+new Intl.PluralRules([deDE, jaJP]);
+>Intl.PluralRules : Symbol(Intl.PluralRules, Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>PluralRules : Symbol(Intl.PluralRules, Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --))
+>deDE : Symbol(deDE, Decl(localesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(localesObjectArgument.ts, 2, 5))
+
+Intl.PluralRules.supportedLocalesOf(enUS);
+>Intl.PluralRules.supportedLocalesOf : Symbol(Intl.PluralRulesConstructor.supportedLocalesOf, Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl.PluralRules : Symbol(Intl.PluralRules, Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>PluralRules : Symbol(Intl.PluralRules, Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --))
+>supportedLocalesOf : Symbol(Intl.PluralRulesConstructor.supportedLocalesOf, Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>enUS : Symbol(enUS, Decl(localesObjectArgument.ts, 0, 5))
+
+Intl.PluralRules.supportedLocalesOf([deDE, jaJP]);
+>Intl.PluralRules.supportedLocalesOf : Symbol(Intl.PluralRulesConstructor.supportedLocalesOf, Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl.PluralRules : Symbol(Intl.PluralRules, Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>PluralRules : Symbol(Intl.PluralRules, Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --))
+>supportedLocalesOf : Symbol(Intl.PluralRulesConstructor.supportedLocalesOf, Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>deDE : Symbol(deDE, Decl(localesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(localesObjectArgument.ts, 2, 5))
+
+new Intl.RelativeTimeFormat(enUS);
+>Intl.RelativeTimeFormat : Symbol(Intl.RelativeTimeFormat, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>RelativeTimeFormat : Symbol(Intl.RelativeTimeFormat, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>enUS : Symbol(enUS, Decl(localesObjectArgument.ts, 0, 5))
+
+new Intl.RelativeTimeFormat([deDE, jaJP]);
+>Intl.RelativeTimeFormat : Symbol(Intl.RelativeTimeFormat, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>RelativeTimeFormat : Symbol(Intl.RelativeTimeFormat, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>deDE : Symbol(deDE, Decl(localesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(localesObjectArgument.ts, 2, 5))
+
+Intl.RelativeTimeFormat.supportedLocalesOf(enUS);
+>Intl.RelativeTimeFormat.supportedLocalesOf : Symbol(supportedLocalesOf, Decl(lib.es2020.intl.d.ts, --, --))
+>Intl.RelativeTimeFormat : Symbol(Intl.RelativeTimeFormat, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>RelativeTimeFormat : Symbol(Intl.RelativeTimeFormat, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>supportedLocalesOf : Symbol(supportedLocalesOf, Decl(lib.es2020.intl.d.ts, --, --))
+>enUS : Symbol(enUS, Decl(localesObjectArgument.ts, 0, 5))
+
+Intl.RelativeTimeFormat.supportedLocalesOf([deDE, jaJP]);
+>Intl.RelativeTimeFormat.supportedLocalesOf : Symbol(supportedLocalesOf, Decl(lib.es2020.intl.d.ts, --, --))
+>Intl.RelativeTimeFormat : Symbol(Intl.RelativeTimeFormat, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>RelativeTimeFormat : Symbol(Intl.RelativeTimeFormat, Decl(lib.es2020.intl.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>supportedLocalesOf : Symbol(supportedLocalesOf, Decl(lib.es2020.intl.d.ts, --, --))
+>deDE : Symbol(deDE, Decl(localesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(localesObjectArgument.ts, 2, 5))
+
+new Intl.Collator(enUS);
+>Intl.Collator : Symbol(Intl.Collator, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>Collator : Symbol(Intl.Collator, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>enUS : Symbol(enUS, Decl(localesObjectArgument.ts, 0, 5))
+
+new Intl.Collator([deDE, jaJP]);
+>Intl.Collator : Symbol(Intl.Collator, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>Collator : Symbol(Intl.Collator, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>deDE : Symbol(deDE, Decl(localesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(localesObjectArgument.ts, 2, 5))
+
+Intl.Collator.supportedLocalesOf(enUS);
+>Intl.Collator.supportedLocalesOf : Symbol(Intl.CollatorConstructor.supportedLocalesOf, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl.Collator : Symbol(Intl.Collator, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>Collator : Symbol(Intl.Collator, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>supportedLocalesOf : Symbol(Intl.CollatorConstructor.supportedLocalesOf, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>enUS : Symbol(enUS, Decl(localesObjectArgument.ts, 0, 5))
+
+Intl.Collator.supportedLocalesOf([deDE, jaJP]);
+>Intl.Collator.supportedLocalesOf : Symbol(Intl.CollatorConstructor.supportedLocalesOf, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl.Collator : Symbol(Intl.Collator, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>Collator : Symbol(Intl.Collator, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
+>supportedLocalesOf : Symbol(Intl.CollatorConstructor.supportedLocalesOf, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>deDE : Symbol(deDE, Decl(localesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(localesObjectArgument.ts, 2, 5))
+
+new Intl.DateTimeFormat(enUS);
+>Intl.DateTimeFormat : Symbol(Intl.DateTimeFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>DateTimeFormat : Symbol(Intl.DateTimeFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --))
+>enUS : Symbol(enUS, Decl(localesObjectArgument.ts, 0, 5))
+
+new Intl.DateTimeFormat([deDE, jaJP]);
+>Intl.DateTimeFormat : Symbol(Intl.DateTimeFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>DateTimeFormat : Symbol(Intl.DateTimeFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --))
+>deDE : Symbol(deDE, Decl(localesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(localesObjectArgument.ts, 2, 5))
+
+Intl.DateTimeFormat.supportedLocalesOf(enUS);
+>Intl.DateTimeFormat.supportedLocalesOf : Symbol(Intl.DateTimeFormatConstructor.supportedLocalesOf, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl.DateTimeFormat : Symbol(Intl.DateTimeFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>DateTimeFormat : Symbol(Intl.DateTimeFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --))
+>supportedLocalesOf : Symbol(Intl.DateTimeFormatConstructor.supportedLocalesOf, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>enUS : Symbol(enUS, Decl(localesObjectArgument.ts, 0, 5))
+
+Intl.DateTimeFormat.supportedLocalesOf([deDE, jaJP]);
+>Intl.DateTimeFormat.supportedLocalesOf : Symbol(Intl.DateTimeFormatConstructor.supportedLocalesOf, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl.DateTimeFormat : Symbol(Intl.DateTimeFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>DateTimeFormat : Symbol(Intl.DateTimeFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --))
+>supportedLocalesOf : Symbol(Intl.DateTimeFormatConstructor.supportedLocalesOf, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>deDE : Symbol(deDE, Decl(localesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(localesObjectArgument.ts, 2, 5))
+
+new Intl.NumberFormat(enUS);
+>Intl.NumberFormat : Symbol(Intl.NumberFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.bigint.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>NumberFormat : Symbol(Intl.NumberFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.bigint.d.ts, --, --))
+>enUS : Symbol(enUS, Decl(localesObjectArgument.ts, 0, 5))
+
+new Intl.NumberFormat([deDE, jaJP]);
+>Intl.NumberFormat : Symbol(Intl.NumberFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.bigint.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>NumberFormat : Symbol(Intl.NumberFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.bigint.d.ts, --, --))
+>deDE : Symbol(deDE, Decl(localesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(localesObjectArgument.ts, 2, 5))
+
+Intl.NumberFormat.supportedLocalesOf(enUS);
+>Intl.NumberFormat.supportedLocalesOf : Symbol(Intl.NumberFormatConstructor.supportedLocalesOf, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl.NumberFormat : Symbol(Intl.NumberFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.bigint.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>NumberFormat : Symbol(Intl.NumberFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.bigint.d.ts, --, --))
+>supportedLocalesOf : Symbol(Intl.NumberFormatConstructor.supportedLocalesOf, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>enUS : Symbol(enUS, Decl(localesObjectArgument.ts, 0, 5))
+
+Intl.NumberFormat.supportedLocalesOf([deDE, jaJP]);
+>Intl.NumberFormat.supportedLocalesOf : Symbol(Intl.NumberFormatConstructor.supportedLocalesOf, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>Intl.NumberFormat : Symbol(Intl.NumberFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.bigint.d.ts, --, --))
+>Intl : Symbol(Intl, Decl(lib.es5.d.ts, --, --), Decl(lib.es2016.intl.d.ts, --, --), Decl(lib.es2017.intl.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2019.intl.d.ts, --, --) ... and 2 more)
+>NumberFormat : Symbol(Intl.NumberFormat, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2018.intl.d.ts, --, --), Decl(lib.es2020.bigint.d.ts, --, --))
+>supportedLocalesOf : Symbol(Intl.NumberFormatConstructor.supportedLocalesOf, Decl(lib.es5.d.ts, --, --), Decl(lib.es2020.intl.d.ts, --, --))
+>deDE : Symbol(deDE, Decl(localesObjectArgument.ts, 1, 5))
+>jaJP : Symbol(jaJP, Decl(localesObjectArgument.ts, 2, 5))
+
diff --git a/tests/baselines/reference/localesObjectArgument.types b/tests/baselines/reference/localesObjectArgument.types
index d7e428d179442..075b79567ff01 100644
--- a/tests/baselines/reference/localesObjectArgument.types
+++ b/tests/baselines/reference/localesObjectArgument.types
@@ -38,6 +38,10 @@ const bigint = 123456789123456789n;
 >bigint : 123456789123456789n
 >123456789123456789n : 123456789123456789n
 
+const str = "";
+>str : ""
+>"" : ""
+
 now.toLocaleString(enUS);
 >now.toLocaleString(enUS) : string
 >now.toLocaleString : { (): string; (locales?: string | string[], options?: Intl.DateTimeFormatOptions): string; (locales?: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions): string; }
@@ -118,3 +122,233 @@ bigint.toLocaleString([deDE, jaJP]);
 >deDE : Intl.Locale
 >jaJP : Intl.Locale
 
+str.toLocaleLowerCase(enUS);
+>str.toLocaleLowerCase(enUS) : string
+>str.toLocaleLowerCase : { (locales?: string | string[]): string; (locales?: Intl.LocalesArgument): string; }
+>str : ""
+>toLocaleLowerCase : { (locales?: string | string[]): string; (locales?: Intl.LocalesArgument): string; }
+>enUS : Intl.Locale
+
+str.toLocaleLowerCase([deDE, jaJP]);
+>str.toLocaleLowerCase([deDE, jaJP]) : string
+>str.toLocaleLowerCase : { (locales?: string | string[]): string; (locales?: Intl.LocalesArgument): string; }
+>str : ""
+>toLocaleLowerCase : { (locales?: string | string[]): string; (locales?: Intl.LocalesArgument): string; }
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
+str.toLocaleUpperCase(enUS);
+>str.toLocaleUpperCase(enUS) : string
+>str.toLocaleUpperCase : { (locales?: string | string[]): string; (locales?: Intl.LocalesArgument): string; }
+>str : ""
+>toLocaleUpperCase : { (locales?: string | string[]): string; (locales?: Intl.LocalesArgument): string; }
+>enUS : Intl.Locale
+
+str.toLocaleUpperCase([deDE, jaJP]);
+>str.toLocaleUpperCase([deDE, jaJP]) : string
+>str.toLocaleUpperCase : { (locales?: string | string[]): string; (locales?: Intl.LocalesArgument): string; }
+>str : ""
+>toLocaleUpperCase : { (locales?: string | string[]): string; (locales?: Intl.LocalesArgument): string; }
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
+str.localeCompare(str, enUS);
+>str.localeCompare(str, enUS) : number
+>str.localeCompare : { (that: string): number; (that: string, locales?: string | string[], options?: Intl.CollatorOptions): number; (that: string, locales?: Intl.LocalesArgument, options?: Intl.CollatorOptions): number; }
+>str : ""
+>localeCompare : { (that: string): number; (that: string, locales?: string | string[], options?: Intl.CollatorOptions): number; (that: string, locales?: Intl.LocalesArgument, options?: Intl.CollatorOptions): number; }
+>str : ""
+>enUS : Intl.Locale
+
+str.localeCompare(str, [deDE, jaJP]);
+>str.localeCompare(str, [deDE, jaJP]) : number
+>str.localeCompare : { (that: string): number; (that: string, locales?: string | string[], options?: Intl.CollatorOptions): number; (that: string, locales?: Intl.LocalesArgument, options?: Intl.CollatorOptions): number; }
+>str : ""
+>localeCompare : { (that: string): number; (that: string, locales?: string | string[], options?: Intl.CollatorOptions): number; (that: string, locales?: Intl.LocalesArgument, options?: Intl.CollatorOptions): number; }
+>str : ""
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
+new Intl.PluralRules(enUS);
+>new Intl.PluralRules(enUS) : Intl.PluralRules
+>Intl.PluralRules : Intl.PluralRulesConstructor
+>Intl : typeof Intl
+>PluralRules : Intl.PluralRulesConstructor
+>enUS : Intl.Locale
+
+new Intl.PluralRules([deDE, jaJP]);
+>new Intl.PluralRules([deDE, jaJP]) : Intl.PluralRules
+>Intl.PluralRules : Intl.PluralRulesConstructor
+>Intl : typeof Intl
+>PluralRules : Intl.PluralRulesConstructor
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
+Intl.PluralRules.supportedLocalesOf(enUS);
+>Intl.PluralRules.supportedLocalesOf(enUS) : string[]
+>Intl.PluralRules.supportedLocalesOf : { (locales: string | string[], options?: { localeMatcher?: "lookup" | "best fit"; }): string[]; (locales: Intl.LocalesArgument, options?: { localeMatcher?: "lookup" | "best fit"; }): string[]; }
+>Intl.PluralRules : Intl.PluralRulesConstructor
+>Intl : typeof Intl
+>PluralRules : Intl.PluralRulesConstructor
+>supportedLocalesOf : { (locales: string | string[], options?: { localeMatcher?: "lookup" | "best fit"; }): string[]; (locales: Intl.LocalesArgument, options?: { localeMatcher?: "lookup" | "best fit"; }): string[]; }
+>enUS : Intl.Locale
+
+Intl.PluralRules.supportedLocalesOf([deDE, jaJP]);
+>Intl.PluralRules.supportedLocalesOf([deDE, jaJP]) : string[]
+>Intl.PluralRules.supportedLocalesOf : { (locales: string | string[], options?: { localeMatcher?: "lookup" | "best fit"; }): string[]; (locales: Intl.LocalesArgument, options?: { localeMatcher?: "lookup" | "best fit"; }): string[]; }
+>Intl.PluralRules : Intl.PluralRulesConstructor
+>Intl : typeof Intl
+>PluralRules : Intl.PluralRulesConstructor
+>supportedLocalesOf : { (locales: string | string[], options?: { localeMatcher?: "lookup" | "best fit"; }): string[]; (locales: Intl.LocalesArgument, options?: { localeMatcher?: "lookup" | "best fit"; }): string[]; }
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
+new Intl.RelativeTimeFormat(enUS);
+>new Intl.RelativeTimeFormat(enUS) : Intl.RelativeTimeFormat
+>Intl.RelativeTimeFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): Intl.RelativeTimeFormat; supportedLocalesOf(locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): string[]; }
+>Intl : typeof Intl
+>RelativeTimeFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): Intl.RelativeTimeFormat; supportedLocalesOf(locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): string[]; }
+>enUS : Intl.Locale
+
+new Intl.RelativeTimeFormat([deDE, jaJP]);
+>new Intl.RelativeTimeFormat([deDE, jaJP]) : Intl.RelativeTimeFormat
+>Intl.RelativeTimeFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): Intl.RelativeTimeFormat; supportedLocalesOf(locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): string[]; }
+>Intl : typeof Intl
+>RelativeTimeFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): Intl.RelativeTimeFormat; supportedLocalesOf(locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): string[]; }
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
+Intl.RelativeTimeFormat.supportedLocalesOf(enUS);
+>Intl.RelativeTimeFormat.supportedLocalesOf(enUS) : string[]
+>Intl.RelativeTimeFormat.supportedLocalesOf : (locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions) => string[]
+>Intl.RelativeTimeFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): Intl.RelativeTimeFormat; supportedLocalesOf(locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): string[]; }
+>Intl : typeof Intl
+>RelativeTimeFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): Intl.RelativeTimeFormat; supportedLocalesOf(locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): string[]; }
+>supportedLocalesOf : (locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions) => string[]
+>enUS : Intl.Locale
+
+Intl.RelativeTimeFormat.supportedLocalesOf([deDE, jaJP]);
+>Intl.RelativeTimeFormat.supportedLocalesOf([deDE, jaJP]) : string[]
+>Intl.RelativeTimeFormat.supportedLocalesOf : (locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions) => string[]
+>Intl.RelativeTimeFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): Intl.RelativeTimeFormat; supportedLocalesOf(locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): string[]; }
+>Intl : typeof Intl
+>RelativeTimeFormat : { new (locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): Intl.RelativeTimeFormat; supportedLocalesOf(locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions): string[]; }
+>supportedLocalesOf : (locales?: Intl.LocalesArgument, options?: Intl.RelativeTimeFormatOptions) => string[]
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
+new Intl.Collator(enUS);
+>new Intl.Collator(enUS) : Intl.Collator
+>Intl.Collator : Intl.CollatorConstructor
+>Intl : typeof Intl
+>Collator : Intl.CollatorConstructor
+>enUS : Intl.Locale
+
+new Intl.Collator([deDE, jaJP]);
+>new Intl.Collator([deDE, jaJP]) : Intl.Collator
+>Intl.Collator : Intl.CollatorConstructor
+>Intl : typeof Intl
+>Collator : Intl.CollatorConstructor
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
+Intl.Collator.supportedLocalesOf(enUS);
+>Intl.Collator.supportedLocalesOf(enUS) : string[]
+>Intl.Collator.supportedLocalesOf : { (locales: string | string[], options?: Intl.CollatorOptions): string[]; (locales: Intl.LocalesArgument, options?: Intl.CollatorOptions): string[]; }
+>Intl.Collator : Intl.CollatorConstructor
+>Intl : typeof Intl
+>Collator : Intl.CollatorConstructor
+>supportedLocalesOf : { (locales: string | string[], options?: Intl.CollatorOptions): string[]; (locales: Intl.LocalesArgument, options?: Intl.CollatorOptions): string[]; }
+>enUS : Intl.Locale
+
+Intl.Collator.supportedLocalesOf([deDE, jaJP]);
+>Intl.Collator.supportedLocalesOf([deDE, jaJP]) : string[]
+>Intl.Collator.supportedLocalesOf : { (locales: string | string[], options?: Intl.CollatorOptions): string[]; (locales: Intl.LocalesArgument, options?: Intl.CollatorOptions): string[]; }
+>Intl.Collator : Intl.CollatorConstructor
+>Intl : typeof Intl
+>Collator : Intl.CollatorConstructor
+>supportedLocalesOf : { (locales: string | string[], options?: Intl.CollatorOptions): string[]; (locales: Intl.LocalesArgument, options?: Intl.CollatorOptions): string[]; }
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
+new Intl.DateTimeFormat(enUS);
+>new Intl.DateTimeFormat(enUS) : Intl.DateTimeFormat
+>Intl.DateTimeFormat : Intl.DateTimeFormatConstructor
+>Intl : typeof Intl
+>DateTimeFormat : Intl.DateTimeFormatConstructor
+>enUS : Intl.Locale
+
+new Intl.DateTimeFormat([deDE, jaJP]);
+>new Intl.DateTimeFormat([deDE, jaJP]) : Intl.DateTimeFormat
+>Intl.DateTimeFormat : Intl.DateTimeFormatConstructor
+>Intl : typeof Intl
+>DateTimeFormat : Intl.DateTimeFormatConstructor
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
+Intl.DateTimeFormat.supportedLocalesOf(enUS);
+>Intl.DateTimeFormat.supportedLocalesOf(enUS) : string[]
+>Intl.DateTimeFormat.supportedLocalesOf : { (locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; (locales: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions): string[]; }
+>Intl.DateTimeFormat : Intl.DateTimeFormatConstructor
+>Intl : typeof Intl
+>DateTimeFormat : Intl.DateTimeFormatConstructor
+>supportedLocalesOf : { (locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; (locales: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions): string[]; }
+>enUS : Intl.Locale
+
+Intl.DateTimeFormat.supportedLocalesOf([deDE, jaJP]);
+>Intl.DateTimeFormat.supportedLocalesOf([deDE, jaJP]) : string[]
+>Intl.DateTimeFormat.supportedLocalesOf : { (locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; (locales: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions): string[]; }
+>Intl.DateTimeFormat : Intl.DateTimeFormatConstructor
+>Intl : typeof Intl
+>DateTimeFormat : Intl.DateTimeFormatConstructor
+>supportedLocalesOf : { (locales: string | string[], options?: Intl.DateTimeFormatOptions): string[]; (locales: Intl.LocalesArgument, options?: Intl.DateTimeFormatOptions): string[]; }
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
+new Intl.NumberFormat(enUS);
+>new Intl.NumberFormat(enUS) : Intl.NumberFormat
+>Intl.NumberFormat : Intl.NumberFormatConstructor
+>Intl : typeof Intl
+>NumberFormat : Intl.NumberFormatConstructor
+>enUS : Intl.Locale
+
+new Intl.NumberFormat([deDE, jaJP]);
+>new Intl.NumberFormat([deDE, jaJP]) : Intl.NumberFormat
+>Intl.NumberFormat : Intl.NumberFormatConstructor
+>Intl : typeof Intl
+>NumberFormat : Intl.NumberFormatConstructor
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
+Intl.NumberFormat.supportedLocalesOf(enUS);
+>Intl.NumberFormat.supportedLocalesOf(enUS) : string[]
+>Intl.NumberFormat.supportedLocalesOf : { (locales: string | string[], options?: Intl.NumberFormatOptions): string[]; (locales: Intl.LocalesArgument, options?: Intl.NumberFormatOptions): string[]; }
+>Intl.NumberFormat : Intl.NumberFormatConstructor
+>Intl : typeof Intl
+>NumberFormat : Intl.NumberFormatConstructor
+>supportedLocalesOf : { (locales: string | string[], options?: Intl.NumberFormatOptions): string[]; (locales: Intl.LocalesArgument, options?: Intl.NumberFormatOptions): string[]; }
+>enUS : Intl.Locale
+
+Intl.NumberFormat.supportedLocalesOf([deDE, jaJP]);
+>Intl.NumberFormat.supportedLocalesOf([deDE, jaJP]) : string[]
+>Intl.NumberFormat.supportedLocalesOf : { (locales: string | string[], options?: Intl.NumberFormatOptions): string[]; (locales: Intl.LocalesArgument, options?: Intl.NumberFormatOptions): string[]; }
+>Intl.NumberFormat : Intl.NumberFormatConstructor
+>Intl : typeof Intl
+>NumberFormat : Intl.NumberFormatConstructor
+>supportedLocalesOf : { (locales: string | string[], options?: Intl.NumberFormatOptions): string[]; (locales: Intl.LocalesArgument, options?: Intl.NumberFormatOptions): string[]; }
+>[deDE, jaJP] : Intl.Locale[]
+>deDE : Intl.Locale
+>jaJP : Intl.Locale
+
diff --git a/tests/baselines/reference/numberFormatCurrencySign.types b/tests/baselines/reference/numberFormatCurrencySign.types
index 50d198deb8539..b61cddf872e5a 100644
--- a/tests/baselines/reference/numberFormatCurrencySign.types
+++ b/tests/baselines/reference/numberFormatCurrencySign.types
@@ -6,9 +6,9 @@ const str = new Intl.NumberFormat('en-NZ', { style: 'currency', currency: 'NZD',
 >new Intl.NumberFormat('en-NZ', { style: 'currency', currency: 'NZD', currencySign: 'accounting' }).format(999999) : string
 >new Intl.NumberFormat('en-NZ', { style: 'currency', currency: 'NZD', currencySign: 'accounting' }).format : { (value: number): string; (value: number | bigint): string; }
 >new Intl.NumberFormat('en-NZ', { style: 'currency', currency: 'NZD', currencySign: 'accounting' }) : Intl.NumberFormat
->Intl.NumberFormat : { (locales?: string | string[] | undefined, options?: Intl.NumberFormatOptions | undefined): Intl.NumberFormat; new (locales?: string | string[] | undefined, options?: Intl.NumberFormatOptions | undefined): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions | undefined): string[]; readonly prototype: Intl.NumberFormat; }
+>Intl.NumberFormat : Intl.NumberFormatConstructor
 >Intl : typeof Intl
->NumberFormat : { (locales?: string | string[] | undefined, options?: Intl.NumberFormatOptions | undefined): Intl.NumberFormat; new (locales?: string | string[] | undefined, options?: Intl.NumberFormatOptions | undefined): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions | undefined): string[]; readonly prototype: Intl.NumberFormat; }
+>NumberFormat : Intl.NumberFormatConstructor
 >'en-NZ' : "en-NZ"
 >{ style: 'currency', currency: 'NZD', currencySign: 'accounting' } : { style: string; currency: string; currencySign: string; }
 >style : string
diff --git a/tests/baselines/reference/numberFormatCurrencySignResolved.types b/tests/baselines/reference/numberFormatCurrencySignResolved.types
index 054866c57f455..75102f726cb0b 100644
--- a/tests/baselines/reference/numberFormatCurrencySignResolved.types
+++ b/tests/baselines/reference/numberFormatCurrencySignResolved.types
@@ -6,9 +6,9 @@ const options = new Intl.NumberFormat('en-NZ', { style: 'currency', currency: 'N
 >new Intl.NumberFormat('en-NZ', { style: 'currency', currency: 'NZD', currencySign: 'accounting' }).resolvedOptions() : Intl.ResolvedNumberFormatOptions
 >new Intl.NumberFormat('en-NZ', { style: 'currency', currency: 'NZD', currencySign: 'accounting' }).resolvedOptions : { (): Intl.ResolvedNumberFormatOptions; (): Intl.ResolvedNumberFormatOptions; }
 >new Intl.NumberFormat('en-NZ', { style: 'currency', currency: 'NZD', currencySign: 'accounting' }) : Intl.NumberFormat
->Intl.NumberFormat : { (locales?: string | string[] | undefined, options?: Intl.NumberFormatOptions | undefined): Intl.NumberFormat; new (locales?: string | string[] | undefined, options?: Intl.NumberFormatOptions | undefined): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions | undefined): string[]; readonly prototype: Intl.NumberFormat; }
+>Intl.NumberFormat : Intl.NumberFormatConstructor
 >Intl : typeof Intl
->NumberFormat : { (locales?: string | string[] | undefined, options?: Intl.NumberFormatOptions | undefined): Intl.NumberFormat; new (locales?: string | string[] | undefined, options?: Intl.NumberFormatOptions | undefined): Intl.NumberFormat; supportedLocalesOf(locales: string | string[], options?: Intl.NumberFormatOptions | undefined): string[]; readonly prototype: Intl.NumberFormat; }
+>NumberFormat : Intl.NumberFormatConstructor
 >'en-NZ' : "en-NZ"
 >{ style: 'currency', currency: 'NZD', currencySign: 'accounting' } : { style: string; currency: string; currencySign: string; }
 >style : string
diff --git a/tests/cases/conformance/es2020/localesObjectArgument.ts b/tests/cases/conformance/es2020/localesObjectArgument.ts
index a89e22ba91de7..37be75f13d6b2 100644
--- a/tests/cases/conformance/es2020/localesObjectArgument.ts
+++ b/tests/cases/conformance/es2020/localesObjectArgument.ts
@@ -7,6 +7,7 @@ const jaJP = new Intl.Locale("ja-JP");
 const now = new Date();
 const num = 1000;
 const bigint = 123456789123456789n;
+const str = "";
 
 now.toLocaleString(enUS);
 now.toLocaleDateString(enUS);
@@ -20,3 +21,35 @@ num.toLocaleString([deDE, jaJP]);
 
 bigint.toLocaleString(enUS);
 bigint.toLocaleString([deDE, jaJP]);
+
+str.toLocaleLowerCase(enUS);
+str.toLocaleLowerCase([deDE, jaJP]);
+str.toLocaleUpperCase(enUS);
+str.toLocaleUpperCase([deDE, jaJP]);
+str.localeCompare(str, enUS);
+str.localeCompare(str, [deDE, jaJP]);
+
+new Intl.PluralRules(enUS);
+new Intl.PluralRules([deDE, jaJP]);
+Intl.PluralRules.supportedLocalesOf(enUS);
+Intl.PluralRules.supportedLocalesOf([deDE, jaJP]);
+
+new Intl.RelativeTimeFormat(enUS);
+new Intl.RelativeTimeFormat([deDE, jaJP]);
+Intl.RelativeTimeFormat.supportedLocalesOf(enUS);
+Intl.RelativeTimeFormat.supportedLocalesOf([deDE, jaJP]);
+
+new Intl.Collator(enUS);
+new Intl.Collator([deDE, jaJP]);
+Intl.Collator.supportedLocalesOf(enUS);
+Intl.Collator.supportedLocalesOf([deDE, jaJP]);
+
+new Intl.DateTimeFormat(enUS);
+new Intl.DateTimeFormat([deDE, jaJP]);
+Intl.DateTimeFormat.supportedLocalesOf(enUS);
+Intl.DateTimeFormat.supportedLocalesOf([deDE, jaJP]);
+
+new Intl.NumberFormat(enUS);
+new Intl.NumberFormat([deDE, jaJP]);
+Intl.NumberFormat.supportedLocalesOf(enUS);
+Intl.NumberFormat.supportedLocalesOf([deDE, jaJP]);
diff --git a/tests/cases/conformance/es2021/es2021LocalesObjectArgument.ts b/tests/cases/conformance/es2021/es2021LocalesObjectArgument.ts
new file mode 100644
index 0000000000000..00b4bc5ea0548
--- /dev/null
+++ b/tests/cases/conformance/es2021/es2021LocalesObjectArgument.ts
@@ -0,0 +1,10 @@
+// @target: es2021
+
+const enUS = new Intl.Locale("en-US");
+const deDE = new Intl.Locale("de-DE");
+const jaJP = new Intl.Locale("ja-JP");
+
+new Intl.ListFormat(enUS);
+new Intl.ListFormat([deDE, jaJP]);
+Intl.ListFormat.supportedLocalesOf(enUS);
+Intl.ListFormat.supportedLocalesOf([deDE, jaJP]);
diff --git a/tests/cases/conformance/es2022/es2022LocalesObjectArgument.ts b/tests/cases/conformance/es2022/es2022LocalesObjectArgument.ts
new file mode 100644
index 0000000000000..7087ae2eab962
--- /dev/null
+++ b/tests/cases/conformance/es2022/es2022LocalesObjectArgument.ts
@@ -0,0 +1,10 @@
+// @target: es2022
+
+const enUS = new Intl.Locale("en-US");
+const deDE = new Intl.Locale("de-DE");
+const jaJP = new Intl.Locale("ja-JP");
+
+new Intl.Segmenter(enUS);
+new Intl.Segmenter([deDE, jaJP]);
+Intl.Segmenter.supportedLocalesOf(enUS);
+Intl.Segmenter.supportedLocalesOf([deDE, jaJP]);