Formal:
* Je suis désolé(e), je ne parle pas français. (This is the most direct and formal way to say it.)
* Je ne parle pas français, excusez-moi. (This is slightly more polite, emphasizing that you are apologizing for not speaking French.)
Informal:
* Désolé(e), je ne parle pas français. (This is a more casual version of the formal option.)
* Je ne comprends pas le français. (This literally means "I don't understand French," but it conveys the same message.)
You can also use:
* Je parle un peu français, mais... (This means "I speak a little French, but...") and then you can explain that you can't understand or speak enough for the current situation.
It's important to note that "Je suis désolé" means "I am sorry" and "Je m'excuse" means "I apologize." You can use either one, but "Je suis désolé" is more common in this context.
No matter which phrase you choose, it's important to be polite and understanding when communicating with someone who doesn't speak your language.