Hi,

Wikidata is adding support for sitelinks to the Multilingual Wikisource.

There's a discussion there about which language should it use. Currently it's "en", which is not quite correct: technically, the site language of Multilingual Wikisource is English, but most of the content is in other languages.

Ideally, each link should specify the language of the page to which it's linking, but currently this is not possible technically.

Until it's possible, suggestions to use "und" or "mul" have been raised: