<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android">
 <RelativeLayout xmlns:tools="http://schemas.android.com/tools"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
tools:context="com.tnnowu.android.switchlanguage.MainActivity">
 <TextView
 android:id="@+id/titleTextView"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:layout_centerInParent="true"
 android:text="@string/title"
 android:textSize="30sp"
 android:textStyle="bold" />
 <TextView
 android:id="@+id/descTextView"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:layout_below="@+id/titleTextView"
 android:layout_centerHorizontal="true"
 android:layout_marginTop="10dp"
 android:text="@string/desc"
 android:textSize="20sp" />
 </RelativeLayout>
</layout>

<?xml version="1.0" encoding="utf-8"?>
<menu xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 tools:context=".MainActivity">

 <item
 android:id="@+id/language_english"
 android:orderInCategory="100"
 android:title="@string/menu_english" />
 <item
 android:id="@+id/language_simplified_chinese"
 android:orderInCategory="100"
 android:title="@string/menu_simplified_chinese" />
 <item
 android:id="@+id/language_turkish"
 android:orderInCategory="100"
 android:title="@string/menu_turkish" />
 <item
 android:id="@+id/language_japanese"
 android:orderInCategory="100"
 android:title="@string/menu_japanese" />
</menu>

@Override
public boolean onCreateOptionsMenu(Menu menu) {
 getMenuInflater().inflate(R.menu.menu, menu);
 return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
 int id = item.getItemId();
 if (id == R.id.language_english) {
 updateViews("en");
 } else if (id == R.id.language_simplified_chinese) {
 updateViews("zh");
 } else if (id == R.id.language_turkish) {
 updateViews("tr");
 } else if (id == R.id.language_japanese) {
 updateViews("ja");
 }
 return super.onOptionsItemSelected(item);
}

private void updateViews(String languageCode) {
 Context context = LocaleHelper.setLocale(this, languageCode);
 Resources resources = context.getResources();
 mBinding.titleTextView.setText(resources.getString(R.string.title));
 mBinding.descTextView.setText(resources.getString(R.string.desc));
 setTitle(resources.getString(R.string.toolbar_title));
}

public class LocaleHelper {
 private static final String SELECTED_LANGUAGE = "Locale.Helper.Selected.Language";
 public static Context onAttach(Context context) {
 String lang = getPersistedData(context, Locale.getDefault().getLanguage());
 return setLocale(context, lang);
 }
 public static Context onAttach(Context context, String defaultLanguage) {
 String lang = getPersistedData(context, defaultLanguage);
 return setLocale(context, lang);
 }
 public static String getLanguage(Context context) {
 return getPersistedData(context, Locale.getDefault().getLanguage());
 }
 public static Context setLocale(Context context, String language) {
 persist(context, language);
 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.N) {
  return updateResources(context, language);
 }
 return updateResourcesLegacy(context, language);
 }
 private static String getPersistedData(Context context, String defaultLanguage) {
 SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(context);
 return preferences.getString(SELECTED_LANGUAGE, defaultLanguage);
 }
 private static void persist(Context context, String language) {
 SharedPreferences preferences = PreferenceManager.getDefaultSharedPreferences(context);
 SharedPreferences.Editor editor = preferences.edit();
 editor.putString(SELECTED_LANGUAGE, language);
 editor.apply();
 }
 @TargetApi(Build.VERSION_CODES.N)
 private static Context updateResources(Context context, String language) {
 Locale locale = new Locale(language);
 Locale.setDefault(locale);
 Configuration configuration = context.getResources().getConfiguration();
 configuration.setLocale(locale);
 return context.createConfigurationContext(configuration);
 }
 @SuppressWarnings("deprecation")
 private static Context updateResourcesLegacy(Context context, String language) {
 Locale locale = new Locale(language);
 Locale.setDefault(locale);
 Resources resources = context.getResources();
 Configuration configuration = resources.getConfiguration();
 configuration.locale = locale;
 resources.updateConfiguration(configuration, resources.getDisplayMetrics());
 return context;
 }
}

public class BaseApplication extends Application {
 @Override
 protected void attachBaseContext(Context base) {
 super.attachBaseContext(LocaleHelper.onAttach(base, "en"));
 }
}