Switching Localizations in iOS is a hassle, doing the Settings -> General -> International -> Choose Language dance is anything but fun.
Luckily for us Xcode provides a great way to switch between Languages easily.
All you have to do is duplicate your Scheme and add these arguments.
For the language:
For the region (time, currency and others):
And as a BONUS, you can tell Xcode to WARN YOU if you don't have localized strings, this will appear in your Console and they will be UPPERCASE in the app:
Check the sample project in Github.