How do you say is that not so in french?

There are a few ways to say "Is that not so?" in French, depending on the context and level of formality:

Formal:

* N'est-ce pas ? (This is the most common and versatile way to say it.)

* N'est-ce point ? (Slightly more formal than "N'est-ce pas?")

Informal:

* C'est pas ça ? (This is more colloquial and less formal)

* Non ? (This simply means "No?" but can be used to ask for confirmation, similar to "Is that not so?")

Example:

* "Il fait beau aujourd'hui, n'est-ce pas ?" (It's beautiful weather today, isn't it?)

* "Tu aimes le chocolat, non ?" (You like chocolate, don't you?)

The best choice depends on the situation and your relationship with the person you're speaking to.