Formal:
* Bilingue: This is the most common and formal way to say "bilingual."
* Bilingue dans (language 1) et (language 2): This is more specific and indicates which two languages the person is fluent in. For example, "Bilingue dans le français et l'anglais" means "Bilingual in French and English."
Informal:
* Parlant deux langues: This literally means "speaking two languages."
Other options:
* Polyglotte: This word means "polyglot" and refers to someone who speaks more than two languages.
So, depending on the situation and formality level, you can choose the best way to express "bilingual" in French.