I deal with these searches a *lot* looking from Greek Letter Organizations as part of WikiProject:Fraternities and Sororities. the current use case is finding all redirects starting with a greek letter and including Redirects with possibilities

A couple comments. 1) There are probably two separable changes, one to pull from wikidata, the other to pull from the associated article (so that [[:fr:Discussion:Johns_Hopkins_University_Press]] pulls from both the wikidata for [[:fr:Johns_Hopkins_University_Press]] and the actual text for [[:fr:Johns_Hopkins_University_Press]] to look for interwikilinks that haven't been moved to wikidata. If the Wikidata one is easier, that would be fine. 2) In terms of pages that don't exist, what does the code do if one of the articles in a single wikidata entry gets deleted, does it still show the language? If so, then I think include the language regardless, worst that happens is that the user ends up being asked to create a talk page.