Manual:$wgUrlProtocols

Details
Defines the URL protocols that MediaWiki will recognize as valid in wfParseUrl. This is used in lots of places. The most visible effect is it determines what protocols are allowed for external links: unrecognized protocols are ignored, no link is generated. However, it's used in many other places too, including the code for Special:LinkSearch, and utility functions like  that are used in a wide variety of different places.

These examples would not work (because  is not defined as a valid protocol):


 * test://www.example.com
 * [test://www.example.com]
 * [test://www.example.com link text ]

To allow links to local files (which may make sense in an intranet context), put this into your :

Usually you only want to add protocols to this array.

Advanced modification
The default protocols should all be safe to click on (no evil side effects), and removing a protocol from the list will cause URLs using those protocols to become unrecognized in many places throughout the software. In particular, removing 'http://' or other common protocols will probably break huge amounts of stuff. Nevertheless, if you need to do so (for example, you already have a News: namespace), you can do something like this: