[MM-14058] Add support for i18n (#2190)

* Add language files

* Add react-intl, mmjstool, setup for adding translations

* Translated main module

* Translations for renderer

* A few minor fixes

* More fixes

* Add CI, add missing menu translations, other cleanup

* Added setting to manually select the language of the app

* Force English for E2e

* Unit tests

* Fix mmjstool

* Move set language to before update menu

* PR feedback

e2e/modules/environment.js

@@ -95,6 +95,7 @@ const demoConfig = {
     darkMode: false,
     lastActiveTeam: 0,
     spellCheckerLocales: [],
+    appLanguage: 'en',
 };
 
 const demoMattermostConfig = {