During Wikimania, Shani told me the famous "Not in the other language" tool
 doesn't work for Wiktionary (because the tool is based on Wikidata but
Wiktionary uses something called Cognate). On my way to the airport, I
wrote a hacky small thing to make things easier for Wiktionary users that
you can find in . Here's an example, list of French nouns that exist in
German Wiktionary but not in English . The code can be found in  and
needs lots of love if anyone is interested.