refactor: use language code with country for messages

crowdin.yml

@@ -1,4 +1,4 @@
 files:
-  - source: /frontend/messages/en.json
+  - source: /frontend/messages/en-US.json
     translation: /%original_path%/%locale%.json
 pull_request_title: 'chore(translations): update translations via Crowdin'

frontend/project.inlang/settings.json

@@ -2,8 +2,8 @@
   "$schema": "https://inlang.com/schema/project-settings",
   "baseLocale": "en",
   "locales": [
-    "en",
-    "nl"
+    "en-US",
+    "nl-NL"
   ],
   "modules": [
     "https://cdn.jsdelivr.net/npm/@inlang/plugin-message-format@4/dist/index.js",

frontend/src/routes/settings/account/locale-picker.svelte

@@ -8,8 +8,8 @@
 	const currentLocale = getLocale();
 
 	const locales = {
-		en: 'English',
-		nl: 'Nederlands'
+		'en-US': 'English',
+		'nl-NL': 'Nederlands'
 	};
 
 	function updateLocale(locale: Locale) {