On Wikivoyage Special:Version, the link for the Calendar extension goes to a 404:
http://www.wikivoyage.org/tech/Calendar_extension
I'm also unable to find a page describing this extension, even though the author listed is attributed on a few other extensions:
https://www.mediawiki.org/w/index.php?search=Roland+Unger&title=Special%3ASearch
Version: unspecified
Severity: normal