an article in the English language edition of Der Spiegel. A curious bit of news, to think such a legacy from WWI was still living on like that. The reparations were a debt imposed on Germany by the Allied victors in WWI in the Treaty of Versaille. They proved a source of great resentment among the Germans, and provided fuel for the Nazi's in their rise to power.
We have many books about WWI, including some about the Versaille treaty and its imposition of the reparations, for example this 1998 title. JSTOR & Historical Abstracts would be good article sources to use in researching the issue as well.