English, absolutely - it is a requirement of scholarships that applicants must demonstrate sufficient knowledge of English. I think a case could probably be made for German as well, as it is practically the "second language" of Wikimedia projects; no doubt a very significant number of attendees will have sufficient fluency in German.
I still don't think we've received a good answer to the question of whether this is a membership in perpetuity or it is a time-limited membership (i.e., the membership only lasts until the end of June 2016 or some other specified date).