I found a solution, even if a bit extreme...
I clicked on "TranslatedStringKey" in the Editor and edited manually every names and description back into french, based on the french wiki.
It took some time, but the result is perfect. I guess it's the only viable solution that I have found for now. It did the trick for me because I only had a dozen of spells to edit.
However, for someone who is trying to do something like a complete class overhaul, he is up for a very long and demoralizing task.
If you find something more efficient, don't hesitate to complete this thread. And thanks for the help and the answers.
