Drupal doesn't support other calendars, Solar Calendar(Gregorian calendar)
here is some works for supporting it using a module. However, it needs a custom hook to be added, which means editing common.inc
Drupal did a great job supporting RTL languages and include many translations. Now we need to step it up in 8.x
I basically added the custom hoon into common.inc
If you have a better way please do inform me.
PS: this hook can be used for all kinds of Calendar systems, more info http://drupal.org/project/calendar_systems