PLT-1800 Load server side locale from the config.json (#3092)

* PLT-1800 Load server side locale from the config.json

* Add support for locales with country specifics

* Fix localization on served locale file as plain/text

webapp/actions/global_actions.jsx

@@ -392,9 +392,14 @@ export function newLocalizationSelected(locale) {
             translations: en
         });
     } else {
+        const localeInfo = I18n.getLanguageInfo(locale) || I18n.getLanguageInfo(global.window.mm_config.DefaultClientLocale);
+
         Client.getTranslations(
-            I18n.getLanguageInfo(locale).url,
-            (data) => {
+            localeInfo.url,
+            (data, res) => {
+                if (!data && res.text) {
+                    data = JSON.parse(res.text); //eslint-disable-line no-param-reassign
+                }
                 AppDispatcher.handleServerAction({
                     type: ActionTypes.RECEIVED_LOCALE,
                     locale,
@@ -408,10 +413,11 @@ export function newLocalizationSelected(locale) {
     }
 }
 
-export function loadBrowserLocale() {
-    let locale = (navigator.languages && navigator.languages.length > 0 ? navigator.languages[0] :
-        (navigator.language || navigator.userLanguage)).split('-')[0];
-    if (!I18n.getLanguages()[locale]) {
+export function loadDefaultLocale() {
+    const defaultLocale = global.window.mm_config.DefaultClientLocale;
+    let locale = global.window.mm_user ? global.window.mm_user.locale || defaultLocale : defaultLocale;
+
+    if (!I18n.getLanguageInfo(locale)) {
         locale = 'en';
     }
     return newLocalizationSelected(locale);