Fix i18n language fallback for regional languages (#4185)

* Fix i18n language fallback for regional languages

* Add release notes

* Fix test

packages/desktop-client/src/i18n.test.ts

@@ -0,0 +1,81 @@
+import i18n from 'i18next';
+
+import { setI18NextLanguage, availableLanguages } from './i18n';
+
+vi.mock('i18next', () => {
+  const i18nMock = {
+    use: vi.fn().mockReturnThis(),
+    init: vi.fn().mockResolvedValue(undefined),
+    changeLanguage: vi.fn(),
+  };
+  return {
+    default: i18nMock,
+  };
+});
+
+vi.hoisted(vi.resetModules);
+
+describe('setI18NextLanguage', () => {
+  beforeEach(async () => {
+    vi.clearAllMocks();
+  });
+
+  afterEach(vi.unstubAllGlobals);
+
+  test('should set system default language when no language is provided', () => {
+    vi.stubGlobal('navigator', { language: 'uk' });
+
+    setI18NextLanguage('');
+
+    expect(i18n.changeLanguage).toHaveBeenCalledWith('uk');
+  });
+
+  test('should set the provided language if it is available', () => {
+    const language = availableLanguages[0];
+
+    setI18NextLanguage(language);
+
+    expect(i18n.changeLanguage).toHaveBeenCalledWith(language);
+  });
+
+  test('should fallback to English if the provided language is unavailable', () => {
+    vi.spyOn(console, 'error');
+
+    setI18NextLanguage('unknown');
+
+    expect(console.error).toHaveBeenCalledWith(
+      'Unknown locale unknown, falling back to en',
+    );
+    expect(i18n.changeLanguage).toHaveBeenCalledWith('en');
+  });
+
+  test('should successfully use a language with a region code if it is known', () => {
+    const language = 'pt-BR';
+
+    setI18NextLanguage(language);
+
+    expect(i18n.changeLanguage).toHaveBeenCalledWith(language);
+  });
+
+  test('should fallback to base language if the provided language has an unknown region code', () => {
+    vi.spyOn(console, 'error');
+
+    setI18NextLanguage('uk-ZZ');
+
+    expect(console.error).toHaveBeenCalledWith(
+      'Unknown locale uk-ZZ, falling back to uk',
+    );
+    expect(i18n.changeLanguage).toHaveBeenCalledWith('uk');
+  });
+
+  test('should fallback to lowercase language if the provided language has uppercase letters', () => {
+    vi.spyOn(console, 'error');
+
+    setI18NextLanguage('EN');
+
+    expect(console.error).toHaveBeenCalledWith(
+      'Unknown locale EN, falling back to en',
+    );
+    expect(i18n.changeLanguage).toHaveBeenCalledWith('en');
+  });
+});

packages/desktop-client/src/i18n.ts

@@ -14,7 +14,6 @@ const isLanguageAvailable = (language: string) =>
 
 const loadLanguage = (language: string) => {
   if (!isLanguageAvailable(language)) {
-    console.error(`Unknown locale ${language}`);
     throw new Error(`Unknown locale ${language}`);
   }
   return languages[`/locale/${language}.json`]();
@@ -41,26 +40,39 @@ i18n
   });
 
 export const setI18NextLanguage = (language: string) => {
-  if (language === 'en' && !isLanguageAvailable(language)) {
-    // English is always available since we use natural-language keys.
-    return;
-  }
-
   if (!language) {
     // System default
     setI18NextLanguage(navigator.language || 'en');
     return;
   }
 
-  language = language.toLowerCase();
-  if (!availableLanguages.includes(language)) {
-    if (language.includes('-')) {
-      setI18NextLanguage(language.split('-')[0]);
+  if (!isLanguageAvailable(language)) {
+    if (language === 'en') {
+      // English is always available since we use natural-language keys.
       return;
     }
 
-    console.error(`Unknown locale ${language}`);
-    throw new Error(`Unknown locale ${language}`);
+    if (language.includes('-')) {
+      const fallback = language.split('-')[0];
+      console.error(`Unknown locale ${language}, falling back to ${fallback}`);
+      setI18NextLanguage(fallback);
+      return;
+    }
+
+    const lowercaseLanguage = language.toLowerCase();
+    if (lowercaseLanguage !== language) {
+      console.error(
+        `Unknown locale ${language}, falling back to ${lowercaseLanguage}`,
+      );
+      setI18NextLanguage(lowercaseLanguage);
+      return;
+    }
+
+    // Fall back to English
+    console.error(`Unknown locale ${language}, falling back to en`);
+    setI18NextLanguage('en');
+    return;
   }
+
   i18n.changeLanguage(language || 'en');
 };

upcoming-release-notes/4185.md

@@ -0,0 +1,6 @@
+---
+category: Bugfix
+authors: [jfdoming]
+---
+
+Fix i18n language fallback for regional languages