I opened a ticket for enabling Extension:Interwiki (I did it in the github repohttps://github.com/wbstack/mediawiki/, but it's unclear to me what the relation is between that repo and the wb.c Phabricator boardhttps://phabricator.wikimedia.org/project/board/5563/.)
As I understand it: WBStack's repo is where WBStack and initial versions of Wikibase.cloud were developed. Phabricator seems to be where WMDE tracks work, and I have seen tickets filed there get some attention. A new GitHub repo is apparently being used now and per WBStack repo's description, is likely to be made public soon, I'd guess under the WMDE account similar to https://github.com/wmde/wbaas-deploy-public
As such I'm not sure how much attention an issue in the soon-abandoned GitHub will get, but at least it's on record.
FWIW, there are various issues in WBStack's repos such as: https://github.com/wbstack/mediawiki/issues https://github.com/wbstack/ui/issues https://github.com/wbstack/cradle/issues Some may have been migrated to phabricator, but as far as I known most have not been, and I hope they are not "lost" as most of the issues remain relevant (if clearly not that pressing, or they would have been addressed already).
Afterwards I however found that interwiki links are enabled, the abbreviations are just not the shortened ones we might be used to from Wikimedia-wikis.
Ah, yes - it has the default set, just not Wikimedia's set. I figured you might want to add a custom interwiki in which case it is less useful. Unfortunately (but understandably) you can't use Wikipedia to "bounce" non-local interwikis any longer.
-- Laurence 'GreenReaper' Parry - greenreaper.co.ukhttp://greenreaper.co.uk Wikibase Community User Group / WikiFur.com