Here’s a list of German names for places where Germany is not the official language. German has a particularly large number of those (Mailand for Milano, Hermannstadt for Sibiu, Löwen for Leuven). The list is the second edition, prepared under the auspices of the United Nations. It is not exhaustive, but the exonyms in it are in current use.

Ausgewählte Exonyme der deutschen Sprache Deutsche Namen und ihre phonetische Umschriftung
für geographische Objekte in Ländern oder Gebieten ohne deutsche Amtssprache
2. Ausgabe
Selected German Language Exonyms
German names and their phonetic transcription
designating geographical objects
of countries or regions where German is not an official language
Second Edition
Ständiger Ausschuss für geographische Namen (StAGN)
Frankfurt am Main 2002

See also a German article in the BDÜ Info for North-Rhine Westphalia (as it is not officially punctuated): Geographische Namen in der Übersetzung.