How do you say this is not true in french?

There are a few ways to say "this is not true" in French, depending on the context and level of formality:

Formal:

* Ce n'est pas vrai. (This is the most common and literal translation)

* Ceci n'est pas exact. (This is not exact)

* Ceci est faux. (This is false)

* Ceci est erroné. (This is erroneous)

Informal:

* C'est pas vrai! (This is not true!)

* C'est faux! (This is false!)

* C'est pas ça! (That's not it!)

More nuanced:

* Ce n'est pas le cas. (This is not the case)

* Ce n'est pas correct. (This is not correct)

* Il n'en est rien. (That's not the case)

The choice of expression will depend on the specific situation and your relationship with the person you are talking to.