Is a ML degree better than moving abroad?Watch
You'd end up speaking better French if you moved there.
You'd have better qualifications and probably more options if you did a degree.
In my opinion if you move to the country it's really important to follow a language course, at least at first, so that you learn the language correctly. I know one person who moved to France after their A Levels and worked as a waitress. She understands extremely well but can only really do "conversational" French and makes a lot of mistakes. Her written French is now IMO below A Level standard because she's not written anything longer than a text message in France since her A Levels 5 years ago.
Whereas another friend of mine who studied French and Spanish at UCL was excellent at French even right at the beginning of her year abroad. She had learnt the theory in class at uni, and practised in with Frenchies she had met in London. After one week in Paris she spoke better French than most of the ex-pats I knew who had been there for years.
I think without studying it at university you have no structure, so if you do go to France you need to structure your own learning and keep yourself motivated.
Also, remember that a language degree isn't just about learning the language itself. You've got history, culture, politics, translation etc. that you can learn about and specialise in, and the degree itself shows that you're capable of higher study, commitment to your studies, and ability to write a dissertation (although that's not always compulsory).
So yeah, decide what you want: spoken/written skills, interesting experiences, learning about culture etc... and go from there.
Mind you, it is worth serious consideration I think, especially financially. Also, it's worth thinking about how you'd find moving abroad aged 18 - while France isn't very far, the distance can feel difficult if you get homesick/have a family emergency etc.
Get in touch if you want any further advice - I studied French & Italian at UCL, spent my summers working in France, and then spent my year abroad studying in Bordeaux and then Bologna, so have a reasonably amount of expertise about living in France and studying languages!