[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

src/main/Validator.ts

@@ -131,6 +131,7 @@ const configDataSchemaV3 = Joi.object<ConfigV3>({
     alwaysMinimize: Joi.boolean(),
     alwaysClose: Joi.boolean(),
     logLevel: Joi.string().default('info'),
+    appLanguage: Joi.string().allow(''),
 });
 
 // eg. data['community.mattermost.com'] = { data: 'certificate data', issuerName: 'COMODO RSA Domain Validation Secure Server CA'};