Changing language on the fly, in running iOS, programmatically

Question

I\'ve been stackling and googling for hours. And I\'m kind of desperate now. I would like to change the language of my application inside the app not only with the default l

Answer 1

According to Apple guidelines this is not a good idea to change language in the app programmatically, but in case u have no power to change requested behaviour, you can do something like next:

1. Prepare some service to manage your language even after app restart

   enum LanguageName: String {
       case undefined
       case en
       case es
   }
   
   let DynamicLanguageServiceDidDetectLanguageSwitchNotificationKey = "DynamicLanguageServiceDidDetectLanguageSwitchNotificationKey"
   
   func dynamicLocalizableString(_ key: String) -> String {
       return LanguageService.service.dynamicLocalizedString(key)
   }
   
   class LanguageService {
   
       private struct Defaults {
           static let keyAppleLanguage = "AppleLanguages"
           static let keyCurrentLanguage = "KeyCurrentLanguage"
       }
   
       static let service:LanguageService = LanguageService()
   
       var languageCode: String {
           get {
               return language.rawValue
           }
       }
   
       var currentLanguage:LanguageName {
           get {
               var currentLanguage = UserDefaults.standard.object(forKey: Defaults.keyCurrentLanguage)
               if let currentLanguage = currentLanguage as? String {
                   UserDefaults.standard.set([currentLanguage], forKey: Defaults.keyAppleLanguage)
                   UserDefaults.standard.synchronize()
               } else {
                   if let languages = UserDefaults.standard.object(forKey: Defaults.keyAppleLanguage) as? [String] {
                       currentLanguage = languages.first
                   }
               }
               if let currentLanguage = currentLanguage as? String, 
                   let lang = LanguageName(rawValue: currentLanguage) {
                   return lang
               }
               return LanguageName.undefined
           }
       }
   
       func switchToLanguage(_ lang:LanguageName) {
           language = lang
           NotificationCenter.default.post(name: NSNotification.Name(rawValue: DynamicLanguageServiceDidDetectLanguageSwitchNotificationKey), object: nil)
       }
   
       private var localeBundle:Bundle?
   
       fileprivate var language: LanguageName = LanguageName.en {
           didSet {
               let currentLanguage = language.rawValue
   
               UserDefaults.standard.set([currentLanguage], forKey:Defaults.keyAppleLanguage)
               UserDefaults.standard.setValue(currentLanguage, forKey:Defaults.keyCurrentLanguage)
               UserDefaults.standard.synchronize()
   
               setLocaleWithLanguage(currentLanguage)            
           }
       }
   
       // MARK: - LifeCycle
   
       private init() {
           prepareDefaultLocaleBundle()
       }
   
       //MARK: - Private
   
       fileprivate func dynamicLocalizedString(_ key: String) -> String {
           var localizedString = key
           if let bundle = localeBundle {
               localizedString = NSLocalizedString(key, bundle: bundle, comment: "")
           } else {
               localizedString = NSLocalizedString(key, comment: "")
           }
           return localizedString
       }
   
       private func prepareDefaultLocaleBundle() {
           var currentLanguage = UserDefaults.standard.object(forKey: Defaults.keyCurrentLanguage)
           if let currentLanguage = currentLanguage as? String {
               UserDefaults.standard.set([currentLanguage], forKey: Defaults.keyAppleLanguage)
               UserDefaults.standard.synchronize()
           } else {
               if let languages = UserDefaults.standard.object(forKey: Defaults.keyAppleLanguage) as? [String] {
                   currentLanguage = languages.first
               }
           }
   
           if let currentLanguage = currentLanguage as? String {
               updateCurrentLanguageWithName(currentLanguage)
           }
       }
   
       private func updateCurrentLanguageWithName(_ languageName: String) {
           if let lang = LanguageName(rawValue: languageName) {
               language = lang
           }
       }
   
       private func setLocaleWithLanguage(_ selectedLanguage: String) {
           if let pathSelected = Bundle.main.path(forResource: selectedLanguage, ofType: "lproj"),
               let bundleSelected = Bundle(path: pathSelected)  {
               localeBundle = bundleSelected
           } else if let pathDefault = Bundle.main.path(forResource: LanguageName.en.rawValue, ofType: "lproj"),
               let bundleDefault = Bundle(path: pathDefault) {
               localeBundle = bundleDefault
           }
       }
   }
   

2. Add some rules to make sure you UI components will be always updated:

   protocol Localizable {
       func localizeUI()
   }
   

3. Implement them

   class LocalizableViewController: UIViewController {
   
       // MARK: - LifeCycle
   
       override func viewDidLoad() {
           super.viewDidLoad()
   
           NotificationCenter.default.addObserver(self, selector: #selector(self.localizeUI), name: NSNotification.Name(rawValue:DynamicLanguageServiceDidDetectLanguageSwitchNotificationKey), object: nil)
       }
   
       override func viewWillAppear(_ animated: Bool) {
           super.viewWillAppear(animated)
   
           localizeUI()
       }
   
       deinit {
           NotificationCenter.default.removeObserver(self)
       }
   }
   
   extension LocalizableViewController: Localizable {
       // MARK: - Localizable
   
       func localizeUI() {
           fatalError("Must Override to provide inApp localization functionality")
       }
   }
   

4. Inherit any controller u want to conform dynamic app switch functionality and implement localizeUI() func

   final class WelcomeTableViewController: LoadableTableViewController
   

5. Switch language as needed:

   LanguageService.service.switchToLanguage(.en)
   

6. All localizabled string should be set as :

   label.text = dynamicLocalizableString()
   

Note: dont forget to add Localizable.strings with same codes as in LanguageName