Set FIRAuth preferred language code by default.

Author: yramanchuk

FirebaseAuthUI/FUIAuth.m

@@ -92,6 +92,10 @@ + (nullable FUIAuth *)authUIWithAuth:(FIRAuth *)auth {
       if ([auth respondsToSelector:@selector(setAdditionalFrameworkMarker:)]) {
         auth.additionalFrameworkMarker = kFirebaseAuthUIFrameworkMarker;
       }
+      // Update auth with the actual language used in the app.
+      // If localization is not provided by developer, the first localization available,
+      // ordered by the user's preferred order, is used.
+      auth.languageCode = [NSBundle mainBundle].preferredLocalizations.firstObject;
     }
     return authUI;
   }

FirebasePhoneAuthUI/README.md

@@ -60,7 +60,6 @@ To start the authentication flow:
 // Swift
 let phoneProvider = FUIAuth.defaultAuthUI()?.providers.first as! FUIPhoneAuth
 phoneProvider.signIn(withPresenting: currentlyVisibleController, phoneNumber: nil)
-}
 ```
 
 ```objective-c