$c->locale_path = '/path/to/davical/locale/files';
It is possible that you have installed DAViCal in a non-standard manner, and DAViCal can't find it's locale files, or you want it to use some different ones that you're writing to submit to the developers (yes please!). In the normal course of events this should not be a problem, and DAViCal should find it's locale files just fine.
It is recommended that you do not set this unless you need it for reasons that only you will know.
Available from DAViCal version: 0.9.9 and later