Changing locale programatically in Android app is quite a pain. I have spent lot of time to find working solution, that currently works in production.
You need to override context in every Activity but also in your Application class, otherwise you will end up with mixed languages in ui.
So here is mine solution which works up to API 29:
Subclass your MainApplication class from:
abstract class LocalApplication : Application() {
override fun attachBaseContext(base: Context) {
super.attachBaseContext(
base.toLangIfDiff(
PreferenceManager
.getDefaultSharedPreferences(base)
.getString("langPref", "sys")!!
)
)
}
}
Also every Activity from:
abstract class LocalActivity : AppCompatActivity() {
override fun attachBaseContext(newBase: Context) {
super.attachBaseContext(
PreferenceManager
.getDefaultSharedPreferences(base)
.getString("langPref", "sys")!!
)
}
override fun applyOverrideConfiguration(overrideConfiguration: Configuration) {
super.applyOverrideConfiguration(baseContext.resources.configuration)
}
}
Add LocaleExt.kt with next extension functions:
const val SYSTEM_LANG = "sys"
const val ZH_LANG = "zh"
const val SIMPLIFIED_CHINESE_SUFFIX = "rCN"
private fun Context.isAppLangDiff(prefLang: String): Boolean {
val appConfig: Configuration = this.resources.configuration
val sysConfig: Configuration = Resources.getSystem().configuration
val appLang: String = appConfig.localeCompat.language
val sysLang: String = sysConfig.localeCompat.language
return if (SYSTEM_LANG == prefLang) {
appLang != sysLang
} else {
appLang != prefLang
|| ZH_LANG == prefLang
}
}
fun Context.toLangIfDiff(lang: String): Context =
if (this.isAppLangDiff(lang)) {
this.toLang(lang)
} else {
this
}
@Suppress("DEPRECATION")
fun Context.toLang(toLang: String): Context {
val config = Configuration()
val toLocale = langToLocale(toLang)
Locale.setDefault(toLocale)
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
config.setLocale(toLocale)
val localeList = LocaleList(toLocale)
LocaleList.setDefault(localeList)
config.setLocales(localeList)
} else {
config.locale = toLocale
}
return if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
config.setLayoutDirection(toLocale)
this.createConfigurationContext(config)
} else {
this.resources.updateConfiguration(config, this.resources.displayMetrics)
this
}
}
/**
* @param toLang - two character representation of language, could be "sys" - which represents system's locale
*/
fun langToLocale(toLang: String): Locale =
when {
toLang == SYSTEM_LANG ->
Resources.getSystem().configuration.localeCompat
toLang.contains(ZH_LANG) -> when {
toLang.contains(SIMPLIFIED_CHINESE_SUFFIX) ->
Locale.SIMPLIFIED_CHINESE
Build.VERSION.SDK_INT >= Build.VERSION_CODES.N ->
Locale(ZH_LANG, "Hant")
else ->
Locale.TRADITIONAL_CHINESE
}
else -> Locale(toLang)
}
@Suppress("DEPRECATION")
private val Configuration.localeCompat: Locale
get() = if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
this.locales.get(0)
} else {
this.locale
}
Add to your res/values/arrays.xml your supported languages in array:
<string-array name="lang_values" translatable="false">
<item>sys</item> <!-- System default -->
<item>ar</item>
<item>de</item>
<item>en</item>
<item>es</item>
<item>fa</item>
...
<item>zh</item> <!-- Traditional Chinese -->
<item>zh-rCN</item> <!-- Simplified Chinese -->
</string-array>
Here is key points:
- Use
config.setLayoutDirection(toLocale); to change layout direction
when you use RTL locales like Arabic, Persian, etc.
"sys" in the code is a value that means "inherit system default language".- Here "langPref" is a key of preference where you put user current language.
- There is no need to recreate the context if it already uses needed
locale.
- There is no need for
ContextWraper as posted here, just set new context returned from createConfigurationContext as baseContext
- This is very important! When you call
createConfigurationContext you should pass configuration crated from scratch and only with Locale property set. There shouldn't be any other property set to this configuration. Because if we set some other properties for this config (orientation for example), we override that property forever, and our context no longer change this orientation property even if we rotate the screen.
- It is not enough only to
recreate activity when user selects a different language, because applicationContext will remain with old locale and it could provide unexpected behaviour. So listen to preference change and restart whole application task instead:
fun Context.recreateTask() {
this.packageManager
.getLaunchIntentForPackage(context.packageName)
?.let { intent ->
val restartIntent = Intent.makeRestartActivityTask(intent.component)
this.startActivity(restartIntent)
Runtime.getRuntime().exit(0)
}
}
