set default language to 'en_us'

src/Umbraco.Web.UI.Client/src/apps/backoffice/backoffice.element.ts

@@ -46,7 +46,7 @@ export class UmbBackofficeElement extends UmbLitElement {
 		this.consumeContext(UMB_AUTH, (auth) => {
 			this.observe(auth.currentUser, (user) => {
 				if (user) {
-					const languageIsoCode = user.languageIsoCode ?? 'en';
+					const languageIsoCode = user.languageIsoCode ?? 'en_us';
 					localizationContext.setLanguage(languageIsoCode);
 				}
 			});

src/Umbraco.Web.UI.Client/src/packages/core/localization/manifests.ts

@@ -4,13 +4,13 @@ import { ManifestTranslations } from '../extension-registry/models/translations.
 const translationManifests: Array<ManifestTranslations> = [
 	{
 		type: 'translations',
-		alias: 'Umb.Translations.En',
+		alias: 'Umb.Translations.En_US',
 		weight: -100,
 		name: 'English (UK)',
 		meta: {
-			culture: 'en',
+			culture: 'en_us',
 		},
-		loader: () => import('../../../assets/lang/en.json'),
+		loader: () => import('../../../assets/lang/en_us.json'),
 	},
 ];