About the keyboard
One thing about the Ukrainian keyboard. I'm used to typing Cyrillic script in a Macedonian keyboard layout, since that's the Slavic language I know best. However, like in the Latin alphabet, not all languages written in Cyrillic have the same letters. I would suggest adding clickable buttons for the Cyrillic letters that are not shared by all, similar to Swedish having separate buttons for ö, ä and å, for example.
The necessary letters for Ukrainian would be Ґ Є І Ї Й Щ Ь Ю and Я (and if there ever was a Macedonian Duolingo, there would hopefully be additional input for Ѓ Ѕ Ј Љ Њ Ќ and Џ). This would also help anyone typing on a Russian keyboard and would also be something that would hopefully be useful for the Russian Duolingo as well, or any other future version using the Cyrillic script.
Considering that this is feature already exists in Latin alphabet versions, I don't think it should be too difficult to add. But it would be extremely useful (and consistent!).