It looks like it is doing something already, but doesn't work right just yet. Amir, could you give some guidance? Basically, I would need a setup like on Meta or Wikidata - the goal, after all, is to eventually just copy the content over from Spore to Wikilambda once it launches.
Seems to be working now so enabled on the "production" wiki.
At least: meta, m, d, commons, wmf, mw, mediawiki; and then en, de, and preferably all the language codes for the language Wikipedias
commons and mw are default interwikis for all MediaWiki wikis. Added meta/m, d, wmf, mediawiki (I wonder if that should be default too - instead we have mediawikiwiki, which is not super intuitive), w for Wikipedia. Language editions can be accessed via "fake" redirects like w:de:, similar to how it works on Wikimedia wikis other than Wikipedias.