Resources res = activity.getResources();
DisplayMetrics dm = res.getDisplayMetrics();
android.content.res.Configuration conf = res.getConfiguration();

Locale locale = new Locale("vi");
Locale.setDefault(locale);

conf.setLocale(locale);
res.updateConfiguration(conf, dm);

Restart activity:
private void restartActivity() {
    Intent intent = getIntent();
    finish();
    startActivity(intent);
}

 

https://stackoverflow.com/questions/8049207/how-to-refresh-activity-after-changing-language-locale-inside-application

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