"Q: Why did this all take place in the German Court system, rather than the US - where Plaintiff does business as Macmillan, and PGLAF is based?

A: The legal guidance PGLAF received is that US law requires that such proceedings would have taken place in the US, and in fact any attempts at enforcement of the judgement would need to occur in the US Court system. PGLAF already informed Plaintiff and the German Court that the US Court system is the appropriate venue for Plaintiff's concerns. Plaintiff declined."

And, as noted in the article, the German courts would also be bound by international copyright treaties to which Germany is a party.

I do hope that these proceedings are forced to take place in the US, because that would set a precedent, however insignificant, that copyright does not apply in other countries.