Hi,
All the labels and buttons canbe localized by copying the STSEventCal.resx file and rename the copy according to your language code like for German it could be STSEventCal.de.resx, then translate the keys.
The easiest tool to edit the .resx files is Visual Studio, you could get the free Visual Studio Express 2008 SP1.
If you do translate I hope you will send me the translation file so I can include it in future releases.
Best,
Joe