There should be a prop=relatedsites module which provides a list of all the related sites.
This will be extremely useful during the Wikidata migration when trying to connect a Wikivoyage page with the Wikidata one.
For some reason the original version of the mw documentation page claims it uses the API, but I can't find anything in the code to indicate that. (https://www.mediawiki.org/w/index.php?title=Extension:RelatedSites&oldid=595097).
Version: unspecified
Severity: enhancement
Unfortunately I have no experience with the API and how to work with the Git repository so I will give at least two ideas:
(1) The API function should be similar to prop=langlinks (ll)
(2) From the public function onSkinTemplateToolboxEnd( &$skinTpl ) (at the end of RelatedSites.class.php) you can learn how to access to the stored values:
$relatedSites = $this->getCustomData()->getSkinData( $skinTpl, 'RelatedSites' );
if ( count( $relatedSites ) == 0 ) {
return true;
}
$relatedSitesUrls = $this->getRelatedSitesUrls( $relatedSites );
foreach ( (array) $relatedSitesUrls as $url ) {
$href = htmlspecialchars( $url['href'] );
$text = $url['text'];
...
}
Now you can check for Wikipedia and Commons. $url['text'] should contain "Wikipedia", "Wikimedia Commons" and others.
We can probably just make this a page property instead of extension data and that automatically gets us an API.
RelatedSites is being deprecated. See T185206: RelatedSites: Code stewardship review and T128326: Undeploy the RelatedSites extension (used on Wikivoyage).
Unless the plan is to archive the extension after removing its usage on Wikimedia sites, this task is still valid.