Board Thread:Support Requests - Getting Technical/@comment-7981828-20130607211426/@comment-452-20130608165645

Try MediaWiki:editnotice-0.

The 0 refers to the main namespace, if you want to add a message to other namespaces, you need to change the number to correspond with that namespace.

If you add uselang=qqx to the end of any URL, you will be able to see the name of the related mediawiki message (even if it currently isn't used)

For example: MediaWiki_Talk:Editnotice-0?action=edit&uselang=qqx shows:
 * Mediawiki:newarticletext - appears when creating new articles in all namespaces
 * Mediawiki:talkpagetext - appears when editing talk pages in all namespaces
 * Mediawiki:editnotice-9 - appears when editing pages in the "MediaWiki_Talk" namespace

To make a random message, take a look at Extension:RandomSelection