Extension:ExtensionCheck

ExtensionCheck adds a parser function to check whether an extension is installed on the local wiki or on Wikipedia.

Use siprop=extensions to get the list of extensions installed on Wikipedia. Then put them in MediaWiki:WikipediaExtensions with a pipe in front of each item like this: ...
 * Abuse Filter
 * AccountAudit
 * AntiBot
 * AntiSpoof
 * AntiSpoof for CentralAuth
 * ApiSandbox

Now you can use: Cite is on the English Wikipedia.

The "Cite" extension is on the local wiki.