I don't know how recent this news is or if anyone has posted it here before, but it seems that Burg Bilstein, the former venue, is under new management and the Scheibenwelt Convention organisers couldn't find a formula that worked for both of them, so the 2013 German DW Convention has had to be cancelled. http://www.scheibenwelt-convention.de/news.php
However, as they say, there is good news too, as they have apparently found an even better castle for the 2015 Convention. They are not letting on what it is yet, but they have released some "spoiler" pics on FB. The best guess so far is the Wartburg (near Eisenach, Thuringia), which would be brilliant if true. (I have been there: it genuinely dates from the Middle Ages - Martin Luther translated some of the Bible there - but was "improved" by Kaiser Bill to make it even more authentically medieval.
Verence of Lancre, eat your heart out...)