I started working on rules for Welsh in my own branch some 6 years ago, but hit a bit of a barrier with which word dictionary to use, and converting Constraint Grammar into languagetool rules.
I did write a converter for An Gramadoir rules for LanguageTool, mainly for converting the Welsh language rules, but due to concerns with which dictionary should be used, I put this on hold whilst awaiting output from the CorCenCC project.
It would be awesome if this could be picked back up!