Manual:$wgExternalDiffEngine

Details
Name of the external diff engine to use, or false to use the internal engine.

The possible values are:


 * -  if available, PHP implementation else.
 * - Wikimedia's fast difference engine implemented as a PHP/HHVM module.
 * - treated as false for backwards compatibility.


 * any other string is treated as a path to external diff executable.

This setting replaces.