Besides calendar itself this plugin (back- and frontend) is in English, so I've added a translation-file (po/mo).
Frontend is translated now. Labels (name, email, etc) and errormessages (Please enter... etc) are translated. At the moment only in my own language Dutch.
Yes, you can simply change core files into your own language, but with a po/mo translation file it's cleaner :-).
Interested? Please reply.