The basic function of interwiki connection is reciprocal, i.e. if en:page links to fr:page, then fr:page necessarily links back to the en:page.
The reality of Wikimedia Commons project is that the Commons category page links:
- primarily to Wikipedia category pages, if they exist
- alternatively to Wikipedia article pages (for the languages which have not the category page for the item)
- possibly, links to "definition" article can be combined (alternated) with links to "list" article (for the languages which have not the definition article or in the case that the definition article doesn't exist at all - e.g. the Commons category "Writers from Bulgary" can link to the item "List of Bulgarian writers" because there exists no definition article "Bulgarian writer").
Of course, the most systematic solution would be to associate category links and article links to identic item together and to use the property "list of" (its inversion) with inclusion functions to associate the list articles. However, such solutions seem to be very unobtainable for now.
However, some simple, easy and universal tool can help. I would welcome a parser function (something like http://tools.wmflabs.org/commonsinterwiki/cgi-bin/main.py/?id=Q5551050) which would include (generate and display) the interwiki list in wiki syntax unidirectionally, without recording at the Wikidata item page. By default, such interwiki links should work as local links (i.e. the iw links from Wikidata should be prioritized) but some parameter should enable to turn the priority over. Maybe, the function can find also other utilization.
E.g., the Commons page "Category:Berlin" is associated with Q4579913 (Category:Berlin) item page of Wikidata and additionaly (using {{On Wikidata}} template with the proposed parser function], the Commons page can include (display) interwiki links to Q64 (Berlin) for the language versions which have not pages associated with Q4579913.
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