"When I sleep I do not talk."
Translation:Kiedy śpię to nie mówię.
Well, I understood it as while X happens, Y happens (not). And I felt the sentence with sombeody who likes it when their grandmother cooks is exactly the same structure. Because it's not so much causality, x leading to y, but more a simultaneous condition. But gdy was wrong here.
"mówią" is 3rd person plural (they talk), so it's wrong.
Putting "ja" in both clauses is super strange, it's like writing it in caps: "Kiedy JA śpię, JA nie mówię" (hard to make this emphasis with English word being "I", but you get the drift. When I am sleeping, it is I who doesn't speak.