Working through the Ukrainian beta, I'm having a rough time getting all the soft signs in the right places, and mixing up the ye's with the e's, the yu's with the u's.
What Duo really needs to do, for languages with not-Latin alphabets, is build in a transliteration engine like the one Google uses for typing in foreign languages in Gmail, like so:
Start typing in Latin font, a menu of choices of what you're trying to type pops up, and you select the one you were looking for. It then self-inserts as your answer.
This would save users a lot of time, and a lot of "wrong" answers due to guessing at the wrong transliteration when typing answers in Latin font. It would also eliminate the need to download and use other language "keyboards" to make sure the answers are spelled right.