[ADD] French translation

[CubicOtter]

Hello all!
After discovering Massive Decks, I've worked on the integration of the French language, following the tutorial on files to modify.

In terms of methodology, I was helped by ChatGPT for an initial translation, and then reviewed all the strings and modified where needed.

I have not been able to test the deployment, and might add a French default deck later.
Thanks for your work on this project!

[Lattyware]

Looks like there is some duplicated effort here, there is an existing French localisation in #504 - is there a value to combining these or is one a better option? Apologies, this probably could have been avoided if it had been merged through, I haven't been able to get a release out due to time pressures, but do aim to do one when I can.

[CubicOtter]

Hello @Lattyware!
Shoot, I hadn't seen the PR from 2022; that would have saved some time! I quickly scrolled through their version, and it looks like we're very close.

On our side with @ValentinPoupard we tested the release and he fixed some bugs, so we can attest that it's all working well and ready to deploy; I'll go through the other PR, see what was done better there (I like their idea of translating Rando Calrissian's name), and add it here in a commit with the other translator's name as contributor!