Manual:$wgMessageCacheType

Details
Message cache setting.

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


 * CACHE_ANYTHING - Use anything, as long as it works
 * CACHE_NONE - Do not cache
 * CACHE_DB - Store cache objects in the DB
 * CACHE_MEMCACHED - , must specify servers in 
 * CACHE_ACCEL - APC, APCu, WinCache or XCache (support of the latter dropped in version 1.31 and above), whichever is available

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.