Is there a good Creole equivalent for the English word "feedback" ? I have sometimes heard native Creole speakers just say something like "fidbak" but would this be widely understood by all Haitians?

Yeah, we do say "fidbak" sometimes :)
But a Haitian who has not traveled to an English speaking country or has not come in contact with the diaspora would probably not understand it.
The H. Creole word for feedback is replik, reyaksyon, repons, and sometimes we say kritik or kòmantè.

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