I think it's the organizer's prerogative to make such a decision, but I do think it is a very unfortunate one. Many German players do collect the English version (especially if they got into the game upon release last year already, like I did). If there is concern about some players not understanding the English cards, the TO/judges should simply have a reference of the German card texts prepared, so if there's doubt about the text of an English card, they can simply look up the German text. Or simply have a bilingually proficient judge.
I frequently use my English cards against players using the German ones, and there's never been a problem -- either they are familiar with the card or I can translate it for them. I understand that in a tournament setting people may be less likely to trust their opponent's translation of an unfamiliar card, but again, the judge should be able to resolve any disputes.