PLT-6518 Fixed user's locale not being loaded with redux actions (#6359)

* Stopped ManageLanguages component from mutating user

* Removed obsolete reference to mm_user

* PLT-6518 Fixed user's locale not being loaded with redux actions

webapp/stores/localization_store.jsx

@@ -12,7 +12,7 @@ class LocalizationStoreClass extends EventEmitter {
     constructor() {
         super();
 
-        this.currentLocale = 'en';
+        this.currentLocale = '';
         this.currentTranslations = null;
     }