I suppose that the registration is reserved for German citizens because the site is in German only. If this were the case, the site would be available in several languages. I know that for the English subsidiary (fidorbank.uk) they only accept the citizens from the United Kingdom, so another reason to think that they only accept Germans.
If that is the case, and it appears from their forums that it might be too, then what options work or are available?
Bittrex has recently also come on board with fiat withdrawals but I can't find what their minimum is? Bitfinex is $10,000.....Usually the number required or already above it for the transaction to get flagged and more paperwork/answers needed by your bank...