Localizing strings in iOS: default (fallback) language?

Perhaps this should help? -- iPhone: localization / internationalization default strings file

It should fallback to English by default. I've just switched my phone to a language into which my app is not localized, and the text was all in English, as expected.

Important: as @hyperspasm commented : To expand on/rephrase this, the fallback language is the language which was most recently chosen by the user in the device Settings, that is also represented in the app's bundle.

To avoid all those lengthy syntax and more having more descriptive var name for translators, I derived my own helper method L() for translation and falling back to English

NSString * L(NSString * translation_key) {
    NSString * s = NSLocalizedString(translation_key, nil);
    if (![[[NSLocale preferredLanguages] objectAtIndex:0] isEqualToString:@"en"] && [s isEqualToString:translation_key]) {
    NSString * path = [[NSBundle mainBundle] pathForResource:@"en" ofType:@"lproj"];
    NSBundle * languageBundle = [NSBundle bundleWithPath:path];
    s = [languageBundle localizedStringForKey:translation_key value:@"" table:nil];
    }
    return s;
}

My Localizable.strings would look like this

"SOME_ACTION_BUTTON" = "Do action";

So in my code, i would use L(@"SOME_ACTION_BUTTON") to get the correct string

Though sometime the key is longer than the translation itself HELP_BUTTON_IN_NAV_BAR = 'Help' but it saves me a lot of time explaining what it is to whoever is helping me doing the translation

You need to make sure that the value of CFBundleDevelopmentRegion in your Info.plist is the language region that you would like to fallback to. (e.g. "en")