Why does Germany still owe money for the first world war?

From the Guardian

"According to Bild magazine, the first world war will finally end this weekend when Germany pays off the last instalment of the interest it owes on loans it took out in the 1930s to pay £22bn in reparations to the allied powers. The sum would, of course, have been paid off much earlier were it not for Adolf Hitler, who exploited public resentment at the economic crisis caused by said reparations to a) refuse to pay them, and b) kick off a whole other war – leading to a whole other load of reparations. But news that Germany was still paying reparations from 1919 in 2010 does rather prompt the question: what for?"