Kingdom creation is intentional for king-level viceroys. Will look into large Byzzies. banu Abbad being unplayable is extremely bizarre and I do not know why they're unplayable, they aren't a theocracy. I blame Paradox. The localization problem is an Speak English Dammit SWMH problem I presume?
Thanks for the clarification on the Byzantine Empire.
As for the Makurian localization problem, yes, it's with the Speak English Dammit module.