It wouldn't crash if the files were missing, and it could be a red herring if you use keys which are the same in English
NSLocalizedString(@"This is a string in the app", @"Example app string")
vs
NSLocalizedString(@"EXAMPLE_APP_STRING", @"Example app string")
If the strings files were missing and you used the first type of format, the text would look as normal in English. As for your actual problem, ensure you have the file localized and in your target, ensure it is in the copy files build phase, clean and build your app, delete it from your test device, then try again.