Russian language support (#9406)

Co-authored-by: Jack Amadeo <jackamadeo@squareup.com>

ui/desktop/src/i18n/i18n.test.ts

@@ -52,6 +52,16 @@ describe('getLocale', () => {
     expect(getLocale()).toEqual({ locale: 'en-GB', messageLocale: 'en' });
   });
 
+  it('returns Russian when navigator.languages contains ru', () => {
+    vi.stubGlobal('navigator', { languages: ['ru'] });
+    expect(getLocale()).toEqual({ locale: 'ru', messageLocale: 'ru' });
+  });
+
+  it('preserves Russian regional tag for formatting', () => {
+    vi.stubGlobal('navigator', { languages: ['ru-RU'] });
+    expect(getLocale()).toEqual({ locale: 'ru-RU', messageLocale: 'ru' });
+  });
+
   it('supports Turkish from navigator.languages', () => {
     vi.stubGlobal('navigator', { languages: ['tr-TR'] });
     expect(getLocale()).toEqual({ locale: 'tr-TR', messageLocale: 'tr' });

ui/desktop/src/i18n/index.ts

@@ -15,7 +15,7 @@
 export { defineMessages, useIntl } from 'react-intl';
 
 /** The set of locales that have translation catalogs. */
-const SUPPORTED_LOCALES = new Set(['en', 'tr', 'zh-CN']);
+const SUPPORTED_LOCALES = new Set(['en', 'ru', 'tr', 'zh-CN']);
 
 /**
  * Map Simplified Chinese aliases (zh, zh-Hans*, zh-SG, zh-MY) to "zh-CN".