将语言代码(如en_US)翻译成英语(United States)是NSLocale的内置特性，NSLocale并不关心你从哪里获得语言代码。因此，确实没有理由像公认的答案所建议的那样实现自己的翻译。

// Example code - try changing the language codes and see what happens
NSLocale *locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en"];
NSString *l1 = [locale displayNameForKey:NSLocaleIdentifier value:@"en"];
NSString *l2 = [locale displayNameForKey:NSLocaleIdentifier value:@"de"];
NSString *l3 = [locale displayNameForKey:NSLocaleIdentifier value:@"sv"];
NSLog(@"%@, %@, %@", l1, l2, l3);

印刷:英语，德语，瑞典语

迅速:

let languageCode = NSLocale.currentLocale().objectForKey(NSLocaleLanguageCode) as? String

在Swift中，有一个更简单的方法来获得当前应用程序语言:

Locale(identifier: Bundle.main.preferredLocalizations[0]).languageCode!

它可以像这样切换，例如:

let supportUrl: URL = {
    switch Locale(identifier: Bundle.main.preferredLocalizations[0]).languageCode {
    case "de":
        return Constants.supportUrlGerman

    default:
        return Constants.supportUrlEnglish
    }
}

我希望这能有所帮助!

iOS13, Swift 5+， WWDC2019 https://developer.apple.com/videos/play/wwdc2019/403/

用户可以独立于操作系统语言选择应用程序的首选语言。

你可以使用这些:

    // Returns a list of the user's preferred languages.
    // Maybe more than (or none of) your app supports!
    Locale.preferredLanguages

    // a subset of this bundle's localizations, re-ordered into the preferred order
    // for this process's current execution environment; the main bundle's preferred localizations
    // indicate the language (of text) the user is most likely seeing in the UI
    Bundle.main.preferredLocalizations



    // The current running app language
    Bundle.main.preferredLocalizations.first

    // list of language names this bundle appears to be localized to
    Bundle.main.localizations

SWIFT-4

 // To get device default selected language. It will print like short name of zone. For english, en or spain, es.

let language = Bundle.main.preferredLocalizations.first! as NSString
print("device language",language)

根据苹果文档

NSUserDefaults* defs = [NSUserDefaults standardUserDefaults];
NSArray* languages = [defs objectForKey:@"AppleLanguages"];
NSString* preferredLang = [languages objectAtIndex:0];