I think the spat has nothing to with the party groups in the european parliament, who are all a bit unusual on the fringes. The question identity as citizen - identity as member of a cultural group - language as technological and administrative tool versus language as part of heritage and identity are much deeper.

And It can be argued that the still centralising french left is the outsider here.

And is doubtful if dwindling languages can be revived: Just look at Irish. On the other hand look at welsh.
Our communists were quite supportive to the sorabians by the way: Didn't help them much, though

And no I don't think the current position of GroenLinks on the budget has a connection to their position on frisian. (Whatever that position is)