Hi everyone,
As you may know, you can include Sitelinks (also known as interwiki links or interlanguage links) that go from individual Items in Wikidata to pages on other Wikimedia sites including Wikisource https://en.wikipedia.org/wiki/Wikisource. Until now, it was not possible to manage the interwiki links to/from multilingual Wikisource on Wikidata. This was due to the unusual technical setup of multilingual Wikisource as well as the fact that we can only link to one page for a topic on any given wiki (multilingual Wikisource can theoretically have several pages covering the same topic in different languages though this is very rare).
We resolved the technical constraint and starting today you can connect pages on multilingual Wikisource with the other language-specific versions of Wikisource so these interwiki links don't have to be maintained in the wikitext anymore. After adding a sitelink, the sitelink appears on the Item page (in the Sitelinks section) with language code mul. The restriction of only being able to link to one page on multilingual Wikisource per Item stays in place and was considered acceptable based on feedback by the Wikisource community.
This feature was requested by users from the Wikisource community. We hope that it can give them more access to Wikidata and the freedom to add multiple links to different Items.
If you encounter any issues or want to provide feedback, feel free to use this Phabricator ticket https://phabricator.wikimedia.org/T138332.
Cheers,