diff --git a/CHANGELOG.md b/CHANGELOG.md
index 8a65a63..741f407 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,21 @@
 # Changelog
 Strictly follows [Semantic Versioning 2.0.0.](https://semver.org/)
 
+## v1.15.0
+`2024-05-10`\
+\
+🚀 Features:
+- TypeScript `5.4.x` support
+```typescript
+// before
+export type Locale = Intl.BCP47LanguageTag | Intl.BCP47LanguageTag[]; // TS 5.3.x
+// new:
+export type Locale = Intl.LocalesArgument; // TS 5.4.x
+```
+
+🔧 Internal:
+- TypeScript upgrade `5.3.2` -> `5.4.5`
+
 ## v1.14.0
 `2023-12-11`\
 \
diff --git a/package.json b/package.json
index 79adb5a..96d0238 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@dnvgl/i18n",
-  "version": "1.14.0",
+  "version": "1.15.0",
   "description": "A set of functions to support multiple languages/cultures in a browser or Node.js",
   "main": "./lib/index.js",
   "types": "./lib/index.d.ts",
@@ -33,13 +33,14 @@
   },
   "license": "MIT",
   "devDependencies": {
-    "@types/jest": "^29.5.11",
-    "@types/node": "^20.10.3",
+    "@types/jest": "^29.5.12",
+    "@types/node": "^20.12.11",
     "jest": "^29.5.0",
     "jest-environment-jsdom": "^29.5.0",
     "rimraf": "^5.0.1",
-    "ts-jest": "^29.1.1",
+    "ts-jest": "^29.1.2",
     "ts-node": "^10.8.0",
-    "typescript": "^5.3.2"
-  }
+    "typescript": "^5.4.5"
+  },
+  "packageManager": "yarn@1.22.22+sha1.ac34549e6aa8e7ead463a7407e1c7390f61a6610"
 }
diff --git a/src/internal/resolveCollatorLocale.ts b/src/internal/resolveCollatorLocale.ts
index c2a273e..79843da 100644
--- a/src/internal/resolveCollatorLocale.ts
+++ b/src/internal/resolveCollatorLocale.ts
@@ -2,10 +2,10 @@ import { createCollator } from "./createCollator";
 import { LocaleOrCollator } from "../types/locale";
 
 /** @internal */
-export function resolveCollatorLocale(locale?: LocaleOrCollator): Intl.Collator {
-  return !locale 
+export function resolveCollatorLocale(source?: LocaleOrCollator): Intl.Collator {
+  return !source 
     ? createCollator() 
-    : (typeof locale === "string" || Array.isArray(locale))
-      ? createCollator(locale)
-      : locale;
-}
\ No newline at end of file
+    : source instanceof Intl.Collator
+      ? source
+      : createCollator(source);
+}
diff --git a/src/types/locale.ts b/src/types/locale.ts
index f5c091e..4aa7b3a 100644
--- a/src/types/locale.ts
+++ b/src/types/locale.ts
@@ -1,2 +1,2 @@
-export type Locale = Intl.BCP47LanguageTag | Intl.BCP47LanguageTag[]; // HINT: https://en.wikipedia.org/wiki/IETF_language_tag
+export type Locale = Intl.LocalesArgument;
 export type LocaleOrCollator = Locale | Intl.Collator;
\ No newline at end of file
diff --git a/yarn.lock b/yarn.lock
index 1856ef1..4dbe212 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -672,10 +672,10 @@
   dependencies:
     "@types/istanbul-lib-report" "*"
 
-"@types/jest@^29.5.11":
-  version "29.5.11"
-  resolved "https://registry.yarnpkg.com/@types/jest/-/jest-29.5.11.tgz#0c13aa0da7d0929f078ab080ae5d4ced80fa2f2c"
-  integrity sha512-S2mHmYIVe13vrm6q4kN6fLYYAka15ALQki/vgDC3mIukEOx8WJlv0kQPM+d4w8Gp6u0uSdKND04IlTXBv0rwnQ==
+"@types/jest@^29.5.12":
+  version "29.5.12"
+  resolved "https://registry.yarnpkg.com/@types/jest/-/jest-29.5.12.tgz#7f7dc6eb4cf246d2474ed78744b05d06ce025544"
+  integrity sha512-eDC8bTvT/QhYdxJAulQikueigY5AsdBRH2yDKW3yveW7svY3+DzN84/2NUgkw10RTiJbWqZrTtoGVdYlvFJdLw==
   dependencies:
     expect "^29.0.0"
     pretty-format "^29.0.0"
@@ -696,10 +696,10 @@
   dependencies:
     undici-types "~5.26.4"
 
-"@types/node@^20.10.3":
-  version "20.10.4"
-  resolved "https://registry.yarnpkg.com/@types/node/-/node-20.10.4.tgz#b246fd84d55d5b1b71bf51f964bd514409347198"
-  integrity sha512-D08YG6rr8X90YB56tSIuBaddy/UXAA9RKJoFvrsnogAum/0pmjkgi4+2nx96A330FmioegBWmEYQ+syqCFaveg==
+"@types/node@^20.12.11":
+  version "20.12.11"
+  resolved "https://registry.yarnpkg.com/@types/node/-/node-20.12.11.tgz#c4ef00d3507000d17690643278a60dc55a9dc9be"
+  integrity sha512-vDg9PZ/zi+Nqp6boSOT7plNuthRugEKixDv5sFTIpkE89MmNtEArAShI4mxuX2+UrLEe9pxC1vm2cjm9YlWbJw==
   dependencies:
     undici-types "~5.26.4"
 
@@ -2443,7 +2443,16 @@ string-length@^4.0.1:
     char-regex "^1.0.2"
     strip-ansi "^6.0.0"
 
-"string-width-cjs@npm:string-width@^4.2.0", string-width@^4.1.0, string-width@^4.2.0, string-width@^4.2.3:
+"string-width-cjs@npm:string-width@^4.2.0":
+  version "4.2.3"
+  resolved "https://registry.yarnpkg.com/string-width/-/string-width-4.2.3.tgz#269c7117d27b05ad2e536830a8ec895ef9c6d010"
+  integrity sha512-wKyQRQpjJ0sIp62ErSZdGsjMJWsap5oRNihHhu6G7JVO/9jIB6UyevL+tXuOqrng8j/cxKTWyWUwvSTriiZz/g==
+  dependencies:
+    emoji-regex "^8.0.0"
+    is-fullwidth-code-point "^3.0.0"
+    strip-ansi "^6.0.1"
+
+string-width@^4.1.0, string-width@^4.2.0, string-width@^4.2.3:
   version "4.2.3"
   resolved "https://registry.yarnpkg.com/string-width/-/string-width-4.2.3.tgz#269c7117d27b05ad2e536830a8ec895ef9c6d010"
   integrity sha512-wKyQRQpjJ0sIp62ErSZdGsjMJWsap5oRNihHhu6G7JVO/9jIB6UyevL+tXuOqrng8j/cxKTWyWUwvSTriiZz/g==
@@ -2461,7 +2470,14 @@ string-width@^5.0.1, string-width@^5.1.2:
     emoji-regex "^9.2.2"
     strip-ansi "^7.0.1"
 
-"strip-ansi-cjs@npm:strip-ansi@^6.0.1", strip-ansi@^6.0.0, strip-ansi@^6.0.1:
+"strip-ansi-cjs@npm:strip-ansi@^6.0.1":
+  version "6.0.1"
+  resolved "https://registry.yarnpkg.com/strip-ansi/-/strip-ansi-6.0.1.tgz#9e26c63d30f53443e9489495b2105d37b67a85d9"
+  integrity sha512-Y38VPSHcqkFrCpFnQ9vuSXmquuv5oXOKpGeT6aGrr3o3Gc9AlVa6JBfUSOCnbxGGZF+/0ooI7KrPuUSztUdU5A==
+  dependencies:
+    ansi-regex "^5.0.1"
+
+strip-ansi@^6.0.0, strip-ansi@^6.0.1:
   version "6.0.1"
   resolved "https://registry.yarnpkg.com/strip-ansi/-/strip-ansi-6.0.1.tgz#9e26c63d30f53443e9489495b2105d37b67a85d9"
   integrity sha512-Y38VPSHcqkFrCpFnQ9vuSXmquuv5oXOKpGeT6aGrr3o3Gc9AlVa6JBfUSOCnbxGGZF+/0ooI7KrPuUSztUdU5A==
@@ -2564,10 +2580,10 @@ tr46@^3.0.0:
   dependencies:
     punycode "^2.1.1"
 
-ts-jest@^29.1.1:
-  version "29.1.1"
-  resolved "https://registry.yarnpkg.com/ts-jest/-/ts-jest-29.1.1.tgz#f58fe62c63caf7bfcc5cc6472082f79180f0815b"
-  integrity sha512-D6xjnnbP17cC85nliwGiL+tpoKN0StpgE0TeOjXQTU6MVCfsB4v7aW05CgQ/1OywGb0x/oy9hHFnN+sczTiRaA==
+ts-jest@^29.1.2:
+  version "29.1.2"
+  resolved "https://registry.yarnpkg.com/ts-jest/-/ts-jest-29.1.2.tgz#7613d8c81c43c8cb312c6904027257e814c40e09"
+  integrity sha512-br6GJoH/WUX4pu7FbZXuWGKGNDuU7b8Uj77g/Sp7puZV6EXzuByl6JrECvm0MzVzSTkSHWTihsXt+5XYER5b+g==
   dependencies:
     bs-logger "0.x"
     fast-json-stable-stringify "2.x"
@@ -2607,10 +2623,10 @@ type-fest@^0.21.3:
   resolved "https://registry.yarnpkg.com/type-fest/-/type-fest-0.21.3.tgz#d260a24b0198436e133fa26a524a6d65fa3b2e37"
   integrity sha512-t0rzBq87m3fVcduHDUFhKmyyX+9eo6WQjZvf51Ea/M0Q7+T374Jp1aUiyUl0GKxp8M/OETVHSDvmkyPgvX+X2w==
 
-typescript@^5.3.2:
-  version "5.3.3"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-5.3.3.tgz#b3ce6ba258e72e6305ba66f5c9b452aaee3ffe37"
-  integrity sha512-pXWcraxM0uxAS+tN0AG/BF2TyqmHO014Z070UsJ+pFvYuRSq8KH8DmWpnbXe0pEPDHXZV3FcAbJkijJ5oNEnWw==
+typescript@^5.4.5:
+  version "5.4.5"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-5.4.5.tgz#42ccef2c571fdbd0f6718b1d1f5e6e5ef006f611"
+  integrity sha512-vcI4UpRgg81oIRUFwR0WSIHKt11nJ7SAVlYNIu+QpqeyXP+gpQJy/Z4+F0aGxSE4MqwjyXvW/TzgkLAx2AGHwQ==
 
 undici-types@~5.26.4:
   version "5.26.5"
@@ -2698,7 +2714,16 @@ which@^2.0.1:
   dependencies:
     isexe "^2.0.0"
 
-"wrap-ansi-cjs@npm:wrap-ansi@^7.0.0", wrap-ansi@^7.0.0:
+"wrap-ansi-cjs@npm:wrap-ansi@^7.0.0":
+  version "7.0.0"
+  resolved "https://registry.yarnpkg.com/wrap-ansi/-/wrap-ansi-7.0.0.tgz#67e145cff510a6a6984bdf1152911d69d2eb9e43"
+  integrity sha512-YVGIj2kamLSTxw6NsZjoBxfSwsn0ycdesmc4p+Q21c5zPuZ1pl+NfxVdxPtdHvmNVOQ6XSYG4AUtyt/Fi7D16Q==
+  dependencies:
+    ansi-styles "^4.0.0"
+    string-width "^4.1.0"
+    strip-ansi "^6.0.0"
+
+wrap-ansi@^7.0.0:
   version "7.0.0"
   resolved "https://registry.yarnpkg.com/wrap-ansi/-/wrap-ansi-7.0.0.tgz#67e145cff510a6a6984bdf1152911d69d2eb9e43"
   integrity sha512-YVGIj2kamLSTxw6NsZjoBxfSwsn0ycdesmc4p+Q21c5zPuZ1pl+NfxVdxPtdHvmNVOQ6XSYG4AUtyt/Fi7D16Q==