I have found now some solution:
COM_MATUKIO_EVENT_DUPLICATE_SUCCESS
COM_MATUKIO_EVENT_DUPLICATE_FAILURE_
COM_MATUKIO_EVENT_UNPUBLISH_SUCCESS
COM_MATUKIO_EVENT_UNPUBLISH_FAILURE_
don't exist in the langiage files. I have solved it with language overrides.
The problem with COM_MATUKIO_EVENT_SAVED remains. Even when I add it to the language overrides I only get ,,,,,,,,, in the system message.
EDIT: It might be related to this topic:
compojoom.com/forum/104-bug-report/16730...-new-event-in-the-fe
Even if I dont fill in the form, I get an event visible only in the backend.