Sorry for the harsh language, but I cannot help it. The people who are serious about this are nincompoops!
Do any of these dopes realize how difficult it will be to communicate with other people? Slavic languages are hard enough when using a latin script. Cyrillic makes it even more difficult to learn. Ukrainian has the normal и and й, plus i and ї for some reason. It has ґ with the non-deformed г being an "h", I believe (any ukraine dogs can help here?) They could try something like duolingo, but it would be hard with no knowledge and it does not teach important military words or phrases. I do think it will teach you "heads up, faget. btr approaching" in ukrainian.
What would Ukraine even entrust non-nationals with? I would only go if I got a javelin, though it would be hard to get it on the plane back home with me.
What do these people expect to do?