did you find a solution Stephan?
well not really. With the latest releases I am now able to deploy and run the application, but no message gets displayed. In the meantime I switched to
although this one does not support loading messages out of a resource bundle.
If anyone has this problem still, here is an explanation as I noticed it too...
The problem comes becouse you have dependencies on both seam-international....3.0.0.AlphaX and 3.0.0.Final. In alpha Messages was interface. If you compile anything against it it expects interface. However in final it is a class, not interface.
So make sure that you have only 3.0.0.Final in dependencies and none of other packages depends on Alpha.
Seam Faces 3.0.2.Final works fine.