https://bugzilla.wikimedia.org/show_bug.cgi?id=72047
--- Comment #3 from Fabian CommodoreFabianus@gmx.de --- Hmmm that is strange. Can you test it without an apicache? For me all three prefixes are known:
import pywikibot s = pywikibot.Site("cs", "wikipedia") s.interwiki("c")
Site("commons", "commons")
s.interwiki("d")
Site("wikidata", "wikidata")
s.interwiki("outreach")
Site("outreach", "outreach")