Koha provides only a single calendar option - the Gregorian calendar. However, in places like India, the *official* national calendar is not Gregorian, although it is used alongside. Plus in rural parts of country, many people still using the "old" non-Gregorian standard.
It will be nice if Koha can support the option of choosing from multiple calendars. I believe support for Hejri (the Islamic calendar) may also be required for middle-East deployments.