Sorry for posting this here when I've already asked for support on YouTrack, but the issue is being ignored and I'm desperate.
Everything happened when some day, I manually edited the spellcheck dictionnary file of my project for batch adding some words.
After that the IDE detected the change and asked me to restart it. Now the spellcheck won't work anymore on that project. If I enable spellcheck for the project (or enable it on the commit message box) an exception loop begins until crashing.
I tried restoring the dictionnary file, emptying it, deleting it, invalidating caches, etc.
Lots of thanks in advance.