Where was Ein Fall für zwei filmed?
German television series (1981–2013)
Ein Fall für zwei (1981–) was filmed in Wiesbaden and Frankfurt Rhine-Main Metropolitan Region, 2 places named in its German Wikipedia’s Konzept section, in Germany. Wikidata records no filming location for it at all, so the article is the only recorded source. Each place says where its claim comes from.
Places per German Wikipedia's Konzept section
German Wikipedia’s Konzept section names 2 places. Each links to the sentence that says so.

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