Hi all!
As is typical for smaller communities, connecting all the pages to Wikidata items can be a major undertaking. Luckily many users have already used Template:Wikipdia (
https://www.wikidata.org/wiki/Q15632185) to connect Wikisource pages to Wikipedia pages. Because Wikipedia pages are already connected quite well to Wikidata, it is easy to find the common item.
I ran a bot on ar-wikisource and found ~400 inclusions of the template. The bot set ~170 sitelinks. The rest of the pages either already had a sitelink or the corresponding Wikipedia page did not have a Wikidata-item yet.
Having also checked around 30 items by hand I couldn't find any mistakes, which shows that the template is well curated. If anyone would like me to run the bot on another language of Wikisource or share the code just send me a message.