https://wiki.openstreetmap.org/wiki/Key:wikipedia#Secondary_languages
Since wikipedia=lang:* , as wikipedia:lang=*  are possible, added it this way, cuz in Osmand it is displayed as Historischer Marktplatz (Hildesheim) instead of https://commons.wikimedia.org/wiki/Category:Historischer_Marktplatz_(Hildesheim), which i find much more pleasant for the eye as the complete link...
But you're right, in so far as  it should be only used for secondary languages.
Maybe someone should contact Osmand and tell them about that even the first language (wikipedia:lang0*) is displayed as entry and  not as link. 