What you want besides the keyboard is called a locale switch with support for your language.
I choose one at random, you can search for locale related things in the Play Store, this will get you started.
Check out "Enable Language"
https://play.google.com/store/apps/details?id=com.trk.eal
I didn't check it on my phone for your dialects.
This sort of thing doesn't work with all apps, just Android stock.
In my experience with others, it's much easier and more effective when running a CyanogenMod (also called CM) rom.
A few phones come with that, on others you have to root the phone and convert to a CM rom.
May work just fine with other stock and custom roms, sorry I'm not sure, it's been a few years since I've helped someone do this.
Maybe I gave you some ideas for searching not just the Play Store, hope so.
Otherwise, if you can confirm from the CM guys that they support that locale, or find it in a language add-on that you can then use with a locale switcher, you'll be pretty close.
From there we can help with choosing a phone and rooting it if it's required.
Hope this helps.
