Thread:MediaWiki talk:Centralauth-login-progress/Will changes to original language be fed back to upstream?/reply (3)

Yes, it is used, but only on this wiki. The actual source message is MediaWiki:Welcomecreation/en, and if you try to edit it yo get a warning. The wording of messages is a choice of developers, so we can make suggestions but they can't be changed as normal translations. I don't know the technical details, though.