January 28, 2015

How To Change Localization Internally In Your iOS Application

Unfortunately, there’s no official way provided by Apple for this purpose. Let’s look at two methods for solve this problem.

Method 1

Apple provides a way to specify application specific language, by updating the “AppleLanguages” key in NSUserDefaults. For example:

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

For working this method, you’ll have to set it before UIKit initialized.

#import <UIKit/UIKit.h>
#import "AppDelegate.h"

int main(int argc, char * argv[]) {
    @autoreleasepool {
        [[NSUserDefaults standardUserDefaults] setObject:@"fr" forKey:@"AppleLanguages"];
        [[NSUserDefaults standardUserDefaults] synchronize];
        return UIApplicationMain(argc, argv, nil, NSStringFromClass([AppDelegate class]));
    }
}

The problem of this method is that the app has to be relaunched to take effect.

Method 2

The solution is to swap the mainBundle of our application as soon as user changes their language preferences inside the app.

See the category for NSBundle.

Header:

#import <Foundation/Foundation.h>

@interface NSBundle (Language)

+ (void)setLanguage:(NSString *)language;

@end

Implementation:

#import "NSBundle+Language.h"
#import <objc/runtime.h>

static const char kBundleKey = 0;

@interface BundleEx : NSBundle

@end

@implementation BundleEx

- (NSString *)localizedStringForKey:(NSString *)key value:(NSString *)value table:(NSString *)tableName
{
    NSBundle *bundle = objc_getAssociatedObject(self, &kBundleKey);
    if (bundle) {
        return [bundle localizedStringForKey:key value:value table:tableName];
    }
    else {
        return [super localizedStringForKey:key value:value table:tableName];
    }
}

@end

@implementation NSBundle (Language)

+ (void)setLanguage:(NSString *)language
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        object_setClass([NSBundle mainBundle],[BundleEx class]);
    });
    id value = language ? [NSBundle bundleWithPath:[[NSBundle mainBundle] pathForResource:language ofType:@"lproj"]] : nil;
    objc_setAssociatedObject([NSBundle mainBundle], &kBundleKey, value, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

@end

In this method a problem that may arise is updating elements on active screens. You can reload your rootViewController from our application delegate, will always work reliably.

- (void)reloadRootViewController
{
    AppDelegate *delegate = [UIApplication sharedApplication].delegate;
    NSString *storyboardName = @"Main";
    UIStoryboard *storybaord = [UIStoryboard storyboardWithName:storyboardName bundle:nil];
    delegate.window.rootViewController = [storybaord instantiateInitialViewController];
}

All code you can see on github. With simple example.

Please, use for free and like it.

Note: in example project by default the app uses method #2. You can disable this. Just comment define USE_ON_FLY_LOCALIZATION.

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