How to change Locale? Not working on some Devices

i have found my solution , my problem was i'm inserted "fa" in Locale and my String Values Directory name was values-fa-rlIR, so names are different so not worked ,i'm wondering why it's working on some devices!

I'm just change the String Values Directory name from values-fa-rlIR to values-fa and it's working well.

had the same problem. Android Studio names the language folder like values-xx-rXX. Android 6.0 and lower can't handle this so You have to rename the foldername (I did it directly in Windows Explorer) to values-de. Now it works for me on all devices