Immunisation works fine for me, but i dont have Opera installed.
However i guess its again a problem of/with Opera, since we had this into the Forums before.
Make sure you are running the program with sufficent Rights (rightclick->start as Adminsitartor) go to settings (if u see an prompt, answer yes) and open tab languages.
Now select German and click APPLY and OK, close th Window and relaunch the Program to let the language-file been load fully .