At the moment all of the German language works in the Kindle Single Store are translations (or so I am told), but Amazon will be accepting new works from German authors in September 2013 - shortly after Laurenz Bolliger joins Amazon to take over the program. Bolliger is currently the Head of International Literature at the German publisher DuMont Verlag, but he will be leaving his position later this year.
Amazon has has had a lot of success with Kindle Singles since the program launched in 2011. Taking a nontraditional publishing approach and applying content of a nontraditional length has resulted in sales of over 4.5 million Kindle Singles, and now that the program is a proven success Amazon has taken it international.
Assuming Amazon is going to open more Kindle Single Stores in more markets, my guess is that the next Kindle Single Stores will launch in Brazil and Spain. This would be an excellent way to broach the Latin American and South American ebook markets.