Last modified: 2008-12-20 00:57:37 UTC
'wgForceUIMsgAsContentMsg' => array( 'metawiki' => array( 'mainpage', ), ),
Workaround would be to use {{MediaWiki:Mainpage/{{int:Lang}}}} (in [[meta:MediaWiki:Mainpage]] and [[meta:MediaWiki:Sidebar]]); see also bug 16608.
I'd rather not just switch the message to user language, since that will result in a useless empty main page if you pick a language that hasn't had one created...
On the other hand there's not many left without. ;) Let's try it...