Add ability to support language subsets, with only CT and CS enabled for now.

CT - Chinese Traditional
CS - Chinese Simplified

Note that if English subsets like en-GB is enabled in the future, the default 'en' value used throughout the code (including in redux.git) needs to be changed to 'en-US'.

electron/createWindow.js

@@ -3,10 +3,23 @@ import { app, BrowserWindow, dialog, shell, screen } from 'electron';
 import isDev from 'electron-is-dev';
 import windowStateKeeper from 'electron-window-state';
 import SUPPORTED_LANGUAGES from 'constants/supported_languages';
+import { SUPPORTED_SUB_LANGUAGE_CODES, SUB_LANG_CODE_LEN } from 'constants/supported_sub_languages';
 
 import setupBarMenu from './menu/setupBarMenu';
 import * as PAGES from 'constants/pages';
 
+function GetAppLangCode() {
+  // 1. Gets the user locale.
+  // 2. Converts unsupported sub-languages to its primary (e.g. "en-GB" -> "en").
+  //    Note that the primary itself may or may not be a supported language
+  //    (up to clients to verify against SUPPORTED_LANGUAGES).
+  const langCode = app.getLocale();
+  if (langCode.length === SUB_LANG_CODE_LEN && !SUPPORTED_SUB_LANGUAGE_CODES.includes(langCode)) {
+    return langCode.slice(0, 2);
+  }
+  return langCode;
+}
+
 export default appState => {
   // Get primary display dimensions from Electron.
   const { width, height } = screen.getPrimaryDisplay().workAreaSize;
@@ -144,7 +157,7 @@ export default appState => {
       const language =
         storedLanguage && storedLanguage !== 'undefined' && storedLanguage !== 'null'
           ? storedLanguage
-          : app.getLocale().slice(0, 2);
+          : GetAppLangCode();
       if (language !== 'en' && SUPPORTED_LANGUAGES[language]) {
         window.webContents.send('language-set', language);
       }

ui/constants/languages.js

@@ -181,6 +181,8 @@ const LANGUAGES = {
   yo: ['Yoruba', 'Yorùbá'],
   za: ['Zhuang', 'Cuengh / Tôô / 壮语'],
   zh: ['Chinese', '中文'],
+  'zh-CN': ['Chinese (Simplified)', '中文 (简体)'],
+  'zh-TW': ['Chinese (Traditional)', '中文 (繁體)'],
   zu: ['Zulu', 'isiZulu'],
 };
 

ui/constants/supported_languages.js

@@ -3,7 +3,8 @@ import LANGUAGES from './languages';
 const SUPPORTED_LANGUAGES = {
   en: LANGUAGES.en[1],
   da: LANGUAGES.da[1],
-  zh: LANGUAGES.zh[1],
+  'zh-CN': LANGUAGES['zh-CN'][1],
+  'zh-TW': LANGUAGES['zh-TW'][1],
   hr: LANGUAGES.hr[1],
   nl: LANGUAGES.nl[1],
   fr: LANGUAGES.fr[1],
@@ -33,4 +34,6 @@ const SUPPORTED_LANGUAGES = {
   uk: LANGUAGES.uk[1],
 };
 
+// Properties: language code (e.g. 'ja')
+// Values: name of the language in native form (e.g. '日本語')
 export default SUPPORTED_LANGUAGES;

ui/constants/supported_sub_languages.js

@@ -0,0 +1,8 @@
+// https://www.electronjs.org/docs/api/locales
+
+export const SUB_LANG_CODE_LEN = 5;
+
+export const SUPPORTED_SUB_LANGUAGE_CODES = [
+  'zh-CN',
+  'zh-TW',
+];