Translation of UI android (in Kotlin)

Question

I need to translate my UI using Kotlin (for Android). I used this code (every time users run the app):

    val sharedPref: SharedPreferences = getSharedPreferences(UI_LANGUAGE_CHANGED, PRIVATE_MODE)
    var restart: Boolean = sharedPref.getBoolean(UI_LANGUAGE_CHANGED, true)

    var lang = selectedLanguageVar.split("-")[0]
    if (translations_languages.indexOf(lang) == -1) {
        lang = "en"
    }
    //println("-->sel: " + selectedLanguageVar + " -->lang: " + getString(R.string.language))
    //println("-->index: " + translations_languages.indexOf(lang))
    var locale: Locale = Locale(lang)
    Locale.setDefault(locale)
    var res: Resources = resources
    var config: Configuration = res.configuration
    config.setLocale(locale)
    //config.setLayoutDirection(locale)
    //createConfigurationContext(config)
    resources.updateConfiguration(config, resources.displayMetrics)

    if (restart || type == "restart") {
        val intent = Intent(this, RestartActivity::class.java).also {
            startActivity(it)

            finish()
        }
    } else {
        if (type == "start") {
            val intent = Intent(this, RestartActivity::class.java).also {
                startActivity(it)
            }
        }
    }

but it's translated in the selected language JUST when it is a device language when I installed the app. So, for example, I install the app and on my device there are English and French. If I select one of these two languages, it translate correctly, otherwise it doesn't work.

I tried also createConfigurationContext(config) but it doesn't work. Is there a way to translate always in a selected language (independently on device)?

Answer 1

As stated in the comments, changing a language is dependent on the API level you are supporting. This is how we're doing it in my company which supports also since API 23.

We do it by wrapping the context of the single activity we have. In here, I'm changing it to French, but you'd have to decide which locale to use. I think that part is depending on your use case, so I'll leave it out of this answer. Every time you want to change the language you need to recreate the activity. This can easily be done by obtaining an instance of the activity and issuing recreate() on it.

class BaseActivity : AppCompatActivity() {

  override fun attachBaseContext(newBase: Context) {
    super.attachBaseContext(newBase.wrap(Locale.FRENCH))
  }
}

The method that wraps the context is an extension function written like:

fun Context.wrap(desiredLocale: Locale): Context {
  if (Build.VERSION.SDK_INT <= Build.VERSION_CODES.M)
    return getUpdatedContextApi23(desiredLocale)

  return if (Build.VERSION.SDK_INT == Build.VERSION_CODES.N) 
      getUpdatedContextApi24(desiredLocale) 
    else 
      getUpdatedContextApi25(desiredLocale)
}

And here are each of the methods that update the locale depending on the version:

@TargetApi(Build.VERSION_CODES.M)
private fun Context.getUpdatedContextApi23(locale: Locale): Context {
  val configuration = resources.configuration
  configuration.locale = locale
  return createConfigurationContext(configuration)
}

private fun Context.getUpdatedContextApi24(locale: Locale): Context {
  val configuration = resources.configuration
  configuration.setLocale(locale)
  return createConfigurationContext(configuration)
}

@TargetApi(Build.VERSION_CODES.N_MR1)
private fun Context.getUpdatedContextApi25(locale: Locale): Context {
  val localeList = LocaleList(locale)
  val configuration = resources.configuration
  configuration.locales = localeList
  return createConfigurationContext(configuration)
}