If you want to check a current language, use the answer of @Sarpe (@Thorbear):
val language = ConfigurationCompat.getLocales(Resources.getSystem().configuration)?.get(0)?.language
// Check here the language.
val format = if (language == "ru") "d MMMM yyyy ?." else "d MMMM yyyy"
val longDateFormat = SimpleDateFormat(format, Locale.getDefault())