Clearly this particular suit by this particular person is iffy. However, I don’t think this framing is very good: the fact Wikimedia is headquartered elsewhere shouldn’t make it immune from being sued where an affected party lives.
Also, this part of the article seems a bit contradictory:
Just because someone doesn’t like what’s written about them doesn’t give them the right to unmask contributors. And if the plaintiff still believes he’s been wronged by these contributors, he can definitely sue them personally for libel (or whatever). What he has no right to demand is that a third party unmask users simply because it’s the easiest target to hit.
Ok, but how does he sue them personally without knowing who they are? It’s fine to say this shouldn’t be regarded as libel (I agree, it’s a factual point, should be covered by exceptio veritatis or whatever) but I think it’s a bit dishonest to say you can’t hit Wikimedia, go after the individual users; but also, Wikimedia shouldn’t be forced to reveal them.
Much better if the court would consider this information as being accurate and in the public interest.
Of course the GDPR cuts two ways here, because political information is an especially protected category, with certain exceptions (notorious information). So I’m not sure how the information on this person’s affiliation to the far right was obtained and so on.