How do you say wrong in French?

It depends on the context.

for "wrong" as in "incorrect" (ex: this is the wrong answer) then the translation is "faux" (fem:"fausse")

In some cases (esp refering to mistakes) it could also be replaced by "mauvais" ex in the sentence "this is the wrong turn" --> "c'est le mauvais tournant"

If talking about an opinion: "being wrong" then the corresponding verb is "Avoir tort"

For "wrong" as is "unacceptable" (ex: 'is it wrong to question God?') then the translation is "Mal"