Board Thread:Support Requests - Getting Technical/@comment-17121236-20140429132837/@comment-1330470-20140429144310

Well that'd be because Special:SystemMessages isn't actually a page anywhere, I think.

The four relevant pages are:
 * Mediawiki:Welcome-message-user
 * Mediawiki:Welcome-message-anon
 * Mediawiki:Welcome-message-wall-user
 * Mediawiki:Welcome-message-wall-anon

depending on if you use message walls or talk pages