No idiom that I recognize.
Student or Learner
Do we have such idiom in English " its a prophet" ? If so, what does it mean?
I have never heard it. It would be unusual for an object to be a prophet, though it might be said of an animal.
not a teacher
This looks rather like a bad translation of a phrase intended to mean "it's an omen".
Along the lines of an omen, I just wondered whether it might be a substitute phrase.
"It's a prophet" = "It's a Jonah" = "It's bad luck".
(BrE first language speaker.)