In order to run a Wikipedia translation campaign that involves many potential source languages, and many potential target languages, it is necessary to refer to the relevant Wikidata item as the 'central' point of coordination for translations about a topic. However, it is not currently possible to use something like WDQ to ask "does this item exist on xyz wikipedia edition?"
[I'm not sure the best way to phrase this query, but @Magnus know what I'm talking about! Please edit the description if you think it isn't clear. Pinging @daniel for the benefit of someone in Wikidata seeing this.]