Manual:$wgExternalDiffEngine

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

The possible value are:
 * wikidiff2: Wikimedia's fast difference engine implemented as a PHP/HHVM module.
 * wikidiff and wikidiff3 are treated as false for backwards compatibility.
 * any other string is treated as a path to external diff executable

This setting replaces useextdiff>Special:MyLanguage/Manual:$wgUseExternalDiffEngine|$wgUseExternalDiffEngine.