However, you could describe them as:
* Fluent French speakers
* Native French speakers (if they were born and raised in a French-speaking environment)
* Bilingual (if they are fluent in French and another language)
* Francophone (a more formal term for anyone who speaks French)
You can also use more informal terms like:
* Frenchy (although this can be considered slightly derogatory)
* Someone who speaks French like a native
Ultimately, the best way to describe someone who speaks fluent French depends on the context and your desired level of formality.