A significant portion of articles on any wikipedia are about cities, towns, local governments, local businesses, minor celebrities, landmarks, &c. For major locations like New York or Berlin, there will of course be articles in many languages, but other things that are insignificant outside their locality are likely to only have an article in their native language. Take for example the Catalan wikipedia, which contains a large number of stubs with basic info on locations in rural Catalonia. [1] The English-speaking world is vastly larger in land area and population than the German-speaking world, so I speculate that the difference in size is due to the number of location-relevant articles.

[1] http://www.kmjn.org/notes/geographically_dense_wikipedia.htm...