"Who has brought a snake here?"
Translation:Kto przyniósł tu węża?
Well... it's a correct sentence, added. Please note, however, that the emphasis is (usually) at the end. So, normally, we would expect that the new information was that there's some snake here. In your sentence, we know that there's a snake, and you ask who the heck brought it HERE.
Ale, ale... I bet that everyone can say it both way by emphasising the same word. Same goes for the sentence "I am trying to clean here", which is not accepting "Próbuję sprzątać tutaj", only "Próbuję tutaj sprzątać". And there's sentence "This is my mother", which doesn't accept "Oto moja matka". Consider adding that answer among correct ones, too. I know it's hard to put all correct answers to each sentence and I appreciate your work, but some sentences really got me crazy with not accepting actually correct answer. Cheers
Well, everything can be achieved by intonation :) If you find an answer that seems correct is unaccepted, better just comment there, it will be easiest for everyone.