localization - iOS: How to change app language programmatically WITHOUT restarting the app?

Question

When I change the app used language independently on the device language it doesn't take effect until I close the app and restart it. How to not require app to be restarted for loading all nib files and .strings files again depending on the selected language?

I use this to change language at runtime:

NSArray* languages = [NSArray arrayWithObjects:@"ar", @"en", nil]; 
[[NSUserDefaults standardUserDefaults] setObject:languages forKey:@"AppleLanguages"];

Answer 1

This works for me : Swift 4 :

Create a file named BundleExtension.swift and add the following code to it -

var bundleKey: UInt8 = 0

class AnyLanguageBundle: Bundle {

override func localizedString(forKey key: String,
                              value: String?,
                              table tableName: String?) -> String {

    guard let path = objc_getAssociatedObject(self, &bundleKey) as? String,
        let bundle = Bundle(path: path) else {

            return super.localizedString(forKey: key, value: value, table: tableName)
    }

    return bundle.localizedString(forKey: key, value: value, table: tableName)
  }
}

extension Bundle {

class func setLanguage(_ language: String) {

    defer {

        object_setClass(Bundle.main, AnyLanguageBundle.self)
    }

    objc_setAssociatedObject(Bundle.main, &bundleKey,    Bundle.main.path(forResource: language, ofType: "lproj"), .OBJC_ASSOCIATION_RETAIN_NONATOMIC)
  }
}

Now whenever you need to change the language call this method :

func languageButtonAction() {
    // This is done so that network calls now have the Accept-Language as "hi" (Using Alamofire) Check if you can remove these
    UserDefaults.standard.set(["hi"], forKey: "AppleLanguages")
    UserDefaults.standard.synchronize()

    // Update the language by swaping bundle
    Bundle.setLanguage("hi")

    // Done to reintantiate the storyboards instantly
    let storyboard = UIStoryboard.init(name: "Main", bundle: nil)
    UIApplication.shared.keyWindow?.rootViewController = storyboard.instantiateInitialViewController()
}