Manual:WfMsgExt

wfMsgExt is a mediawiki function within GlobalFunctions.php to retrieve the contents of a system message as listed in Special:Allpages

Parameters to wfMsgExt
function wfMsgExt( $key, $options ) can accept the following as options:

Related functions
 * wfMsg
 * wfMsgHtml
 * wfMsgWikiHtml