Manual:$wgMessageCacheType

Details
Message cache setting.

Here are the available CACHE constants, as defined in Defines.php

Use anything, as long as it works Do not cache Store cache objects in the DB , must specify servers in  eAccelerator, mmTurck, APC or XCache, whichever is available
 * CACHE_ANYTHING -
 * CACHE_NONE -
 * CACHE_DB -
 * CACHE_MEMCACHED -
 * CACHE_ACCEL -

As of MediaWiki 1.18, thread>Thread:Project:Support desk/Caching with eAccelerator|current versions of eAccelerator no longer work. In MediaWiki 1.19 it will be removed. Use PHP's DBA extension to store in a DBM-style database
 * CACHE_DBA -

Note
If you set  then the values for  and $wgMessageCacheType will inherit it.

You do not need to set those variables unless you plan on doing something very advanced.