"I am not French, but I speak..."
To complete the sentence and make it grammatically correct, you need to add the language you speak fluently. For example:
* "Je ne suis pas français mais je parle couramment français." (I am not French but I speak French fluently.)
* "Je ne suis pas français mais je parle couramment anglais." (I am not French but I speak English fluently.)
Let me know if you'd like to complete the sentence with a specific language and I can translate it for you!