Not sure, but is this missing {{noexternallanglinks}}?

That being said, could you elaborate on what the motivation behind the module is?

In T303111#9605129, @Michael wrote:

Not sure, but is this missing {{noexternallanglinks}}?

{{noexternallanglinks}} shouldn’t be necessary. If a local interlanguage link is defined, it should override the Wikibase-based one even without the magic word; this works on every other wiki. (E.g. https://hu.wikipedia.org/w/index.php?title=E-d%C3%BAr_heged%C5%B1verseny_(Johann_Sebastian_Bach)&oldid=21583931 shows only the local interlanguage link [[de:Violinkonzerte (Bach)#Violinkonzert E-Dur BWV 1042]] and automatically hides the Wikidata-based [[de:BWV 1042]].)

That being said, could you elaborate on what the motivation behind the module is?

The historical motivation behind the module is that Wikidata hasn’t supported multilingual Wikisource for a long time (T275958).

The reason why I didn’t remove the module call once Wikidata started supporting multilingual Wikisource is that on translations like https://wikisource.org/wiki/Wikisource:WS_Export/de, only the module works (this is not specific to multilingual Wikisource; simply translations are different pages and Wikibase Client handles them as such).