NSLocalizedString() reads the value for the key AppleLanguages from the standard user defaults ([NSUserDefaults standardUserDefaults]). It uses that value to choose an appropriate localization among all existing localizations at runtime. When Apple builds the user defaults dictionary at app launch, they look up the preferred language(s) key in the system preferences and copy the value from there. This also explains for example why changing the language settings in OS X has no effect on running apps, only on apps started thereafter. Once copied, the value is not updated just because the settings change. That's why iOS restarts all apps if you change then language.

但是，用户默认字典的所有值都可以被命令行参数覆盖。请参阅NSArgumentDomain上的NSUserDefaults文档。这甚至包括那些从应用程序首选项(.plist)文件加载的值。如果您只是为了测试而更改一个值，了解这一点非常有用。

所以如果你想改变语言只是为了测试，你可能不想改变你的代码(如果你忘记删除这段代码…)，而是告诉Xcode用一个命令行参数启动你的应用程序(例如使用西班牙语本地化):

根本不需要修改代码。只需为不同的语言创建不同的方案，您可以快速启动应用程序一次在一种语言和一次在另一种只需切换方案。

对于我的案例，我有两个本地化文件，ja和en

如果系统中首选语言既不是en也不是ja，我希望将其强制为en

我要编辑主体部分。m文件

我会检查第一种首选语言是en还是ja，如果不是，那么我会把第二种首选语言改为en。

int main(int argc, char *argv[])
{

    [[NSUserDefaults standardUserDefaults] removeObjectForKey:@"AppleLanguages"];
    [[NSUserDefaults standardUserDefaults] synchronize];

    NSString *lang = [[NSLocale preferredLanguages] objectAtIndex:0];

    if (![lang isEqualToString:@"en"]  &&  ![lang isEqualToString:@"ja"]){

        NSMutableArray *array = [[NSMutableArray alloc] initWithArray:[NSLocale preferredLanguages]];
        [array replaceObjectAtIndex:1 withObject:@"en"];

        [[NSUserDefaults standardUserDefaults] setObject:array forKey:@"AppleLanguages"];
        [[NSUserDefaults standardUserDefaults] synchronize];


    }

    @autoreleasepool {
        return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));


    }


}

Swift 3解决方案:

let languages = ["bs", "zh-Hant", "en", "fi", "ko", "lv", "ms", "pl", "pt-BR", "ru", "sr-Latn", "sk", "es", "tr"]
UserDefaults.standard.set([languages[0]], forKey: "AppleLanguages")

给出了一些可以使用的语言代码的例子。希望这能有所帮助

对于Swift，你可以覆盖main.swift文件，并在应用程序运行之前设置UserDefaults字符串。这样你就不需要重新启动应用程序就能看到想要的效果。

import Foundation
import UIKit

// Your initialisation code here
let langCultureCode: String = "LANGUAGE_CODE"

UserDefaults.standard.set([langCultureCode], forKey: "AppleLanguages")
UserDefaults.standard.synchronize()

UIApplicationMain(CommandLine.argc, CommandLine.unsafeArgv, nil, NSStringFromClass(AppDelegate.self))

同时移除你的AppDelegate.swift文件中的@UIApplicationMain。

请勿在iOS 9上使用。对于所有经过它的字符串返回nil。

我找到了另一个解决方案，允许您更新语言字符串，w/o重新启动应用程序和兼容genstrings:

将这个宏放在Prefix.pch中:

#define currentLanguageBundle [NSBundle bundleWithPath:[[NSBundle mainBundle] pathForResource:[[NSLocale preferredLanguages] objectAtIndex:0] ofType:@"lproj"]]

在任何需要本地化字符串的地方使用:

NSLocalizedStringFromTableInBundle(@"GalleryTitleKey", nil, currentLanguageBundle, @"")

设置语言使用。

[[NSUserDefaults standardUserDefaults] setObject:[NSArray arrayWithObject:@"de"] forKey:@"AppleLanguages"];

即使连续的语言跳跃也能工作，比如:

NSLog(@"test %@", NSLocalizedStringFromTableInBundle(@"NewKey", nil, currentLanguageBundle, @""));
[[NSUserDefaults standardUserDefaults] setObject:[NSArray arrayWithObject:@"fr"] forKey:@"AppleLanguages"];
NSLog(@"test %@", NSLocalizedStringFromTableInBundle(@"NewKey", nil, currentLanguageBundle, @""));
[[NSUserDefaults standardUserDefaults] setObject:[NSArray arrayWithObject:@"it"] forKey:@"AppleLanguages"];
NSLog(@"test %@", NSLocalizedStringFromTableInBundle(@"NewKey", nil, currentLanguageBundle, @""));
[[NSUserDefaults standardUserDefaults] setObject:[NSArray arrayWithObject:@"de"] forKey:@"AppleLanguages"];
NSLog(@"test %@", NSLocalizedStringFromTableInBundle(@"NewKey", nil, currentLanguageBundle, @""));

根据Tudorizer的回答，在不离开或重新启动应用程序的情况下更改语言。

使用类来访问首选语言，而不是宏，以检查是否存在特定的语言代码。

下面是一个类，用于获取当前在iOS 9中工作的语言包:

@implementation OSLocalization

+ (NSBundle *)currentLanguageBundle
{
    // Default language incase an unsupported language is found
    NSString *language = @"en";

    if ([NSLocale preferredLanguages].count) {
        // Check first object to be of type "en","es" etc
        // Codes seen by my eyes: "en-US","en","es-US","es" etc

        NSString *letterCode = [[NSLocale preferredLanguages] objectAtIndex:0];

        if ([letterCode rangeOfString:@"en"].location != NSNotFound) {
            // English
            language = @"en";
        } else if ([letterCode rangeOfString:@"es"].location != NSNotFound) {
            // Spanish
            language = @"es";
        } else if ([letterCode rangeOfString:@"fr"].location != NSNotFound) {
            // French
            language = @"fr";
        } // Add more if needed
    }

    return [NSBundle bundleWithPath:[[NSBundle mainBundle] pathForResource:language ofType:@"lproj"]];
}

/// Check if preferred language is English
+ (BOOL)isCurrentLanguageEnglish
{
    if (![NSLocale preferredLanguages].count) {
        // Just incase check for no items in array
        return YES;
    }

    if ([[[NSLocale preferredLanguages] objectAtIndex:0] rangeOfString:@"en"].location == NSNotFound) {
        // No letter code for english found
        return NO;
    } else {
        // Tis English
        return YES;
    }
}

/*  Swap language between English & Spanish
 *  Could send a string argument to directly pass the new language
 */
+ (void)changeCurrentLanguage
{
    if ([self isCurrentLanguageEnglish]) {
        [[NSUserDefaults standardUserDefaults] setObject:@[@"es"] forKey:@"AppleLanguages"];
    } else {
        [[NSUserDefaults standardUserDefaults] setObject:@[@"en"] forKey:@"AppleLanguages"];
    }
}
@end

使用上面的类来引用一个字符串文件/图像/视频/等等:

// Access a localized image
[[OSLocalization currentLanguageBundle] pathForResource:@"my_image_name.png" ofType:nil]
// Access  a localized string from Localizable.strings file
NSLocalizedStringFromTableInBundle(@"StringKey", nil, [OSLocalization currentLanguageBundle], @"comment")

像下面这样inline更改language或更新上面类中的"changeCurrentLanguage"方法，以获取引用新语言的字符串参数。

[[NSUserDefaults standardUserDefaults] setObject:@[@"es"] forKey:@"AppleLanguages"];