Is he in 2°? What série (ie L ES S or STMG) is he thinking of choosing for the Bac? He will be doing the French bit of the Bac next year in 1°. Depending on which speciality he goes for, he can still get his Bac even with a bad mark for French because of the weightings given to different subjects. I'd say, however, that whether he likes it or not he just has to get on with it and do at least the minimum necessary to get, say, 9 or 10 as that won't penalise him unduly later.
If he refuses to do the work he will get 0 and may well find himself shunted into a course he doesn't like in 1°
a) because he won't have demonstrated an ability to rise above personal likes and dislikes and do his work in order to succeed and
b) he will have demonstrated that he isn't actually that clever (because he hasn't understood a).
Refusing to work seldom goes down well and if, once we have had a few chats about it with colleagues & the pupil in question, a solution isn't found, one of two things will happen - either the pupil continues not to work, does badly, passes & goes somewhere else & isn't our problem any more or he/she doesn't pass and we refuse to take him or her back to resit & he/she won't be our problem any more.
The marks people get are important, obviously, but for entry to good higher education the comments on the report are VERY important and things like 'refuses to work, needs to grow up' will not stand a candidate in good stead.
I teach in lycée and after a while if someone refuses to work then it is up to them, I have 36 people in class and someone who has decided to refuse to work has made his choice and will have to live with the result - I will devote my efforts to those who are willing to make an effort.