"When I sleep I do not talk."
Translation:Kiedy śpię, to nie mówię.
Is there a difference between starting this sentence with "Kiedy" or with "Gdy"? So far, I have seen "kiedy?" as a question, and have not seen "gdy" at all (but it was in the tool tip).
you are right kiedy is a question word, or a word to link two related parts of sentence, gdy only links parts of sentence.
I do not think doulingo tips are even able to differentiate how is a word used in the sentence, otherwise we would not get so many misleading ones
A polish friend says, it's not wrong but emphasizes the "ja" ("I") a lot. Could be considered as a correct answer, i think.
Sure, it's not wrong, but I think it's pretty strange. If you put "ja" before "śpię", then it would simply emphasize "I". But putting "ja" before "nie mówię"... That sounds as if I didn't talk, but other people did...
Sounds plausible. Very likely my friend meant the same "No" in a polite and not discouraging way by saying "it's not wrong, but" ... :-)
It's not necessary (the answer is accepted without it), but it's a useful conjunction. "When X happens, then Y happens". It works like that.