MUC Service sends "disturbing" service messages.
Openfire sends annyoing MUC service message, while entering or creating a MUC room.
There are some more of this kind.
The problem is, that they are in english (or rather in Openfire's language settings), but a client might use any other locale.
Furthermore they might feel annoying to end users, especially if they read messages, not according to their language settings.
XEP-0045: Multi-User Chat does not specify, that any such messages should be sent.
Instead presence stanzas with a status code should be sent.
I removed the messages.
new room creation is already marked with status code 201 in presence.
"is now unlocked" message was not specified by XEP-0045 (instead only an IQ result should be returned to the room creator)
The warning, that a room is non-anonymous is now marked with status code 100 in initial presence (as per XEP-0045).