I would suggest changing this sentence to something other than a name. I had no idea what Matěj was either. Maybe the English sentence could be "young boys" or "young girls".
I was confused by the format of the challenge, I didnt know if i was supposed to type what i was looking at or translate Matéj to english name Mathew. It says "finish the translation" so i translated it but in reality was expected to transcribe the word i was already being given
I don't quite understand the situation you described, but you should never "translate" names. The Czech names, however, are usually accepted in English translations even if you leave out the necessary diacritics.