Admin Forum:How do you change the enter and leave messages for the chat?

So, while on the Mortal Kombat Wiki's chat, I saw that it changed the enter and leave messages, to "UsernameHere has joined the battle" and "UsernameHere has fled the battle" respectively. I want to do this but can't figure out how. Can anyone tell me how to do this? TigerTheDragon12 14:50, March 18, 2012 (UTC)
 * These MediaWiki pages:
 * MediaWiki:Chat-kick-log-reason
 * MediaWiki:Chat-user-parted
 * MediaWiki:Chat-userrightslog-a-made-b-chatmod
 * MediaWiki:Chat-user-was-kickbanned
 * MediaWiki:Chat-user-parted
 * MediaWiki:Chat-user-manu-contribs
 * MediaWiki:Chat-user-manu-profile
 * MediaWiki:Chat-user-manu-private
 * MediaWiki:Chat-user-manu-kickban
 * MediaWiki:Chat-member-since
 * MediaWiki:Chat-private-headline
 * MediaWiki:Chat-start-a-chat
 * MediaWiki:Chat-user-manu-give-chat-mod
 * MediaWiki:Chat-join-the-chat
 * MediaWiki:Chat-edit-count
 * MediaWiki:Chat-user-joined
 * I know you asked for two, but I figured I'd give you the full barrel.