Part of the plan for 4.3 is to implement proper astronomical calender support, which Allen Winter plans to use in a re-write of libkholiday to support such tricky holiday calculations. Showing holidays from a different or multiple calendar systems and locales on a single calendar widget should be fairly easy, I'd just add an API to KDateTable where you pass in the locale that you want the holidays shown for.
You may not be aware of this as I don't think anyone has used it yet, but you can now actually have date widgets set to a different locale and thus calendar system than the global calendar system, i.e. you could have plasmoids on your desktop displaying the Hebrew and Hijri calendars while still keeping Gregorian as your system calendar system. I keep meaning to look at the new plasma calendar widget to see if it supports setting the calendar system, or if I need to add it in.
Part of the plan for 4.3 is
Part of the plan for 4.3 is to implement proper astronomical calender support, which Allen Winter plans to use in a re-write of libkholiday to support such tricky holiday calculations. Showing holidays from a different or multiple calendar systems and locales on a single calendar widget should be fairly easy, I'd just add an API to KDateTable where you pass in the locale that you want the holidays shown for.
You may not be aware of this as I don't think anyone has used it yet, but you can now actually have date widgets set to a different locale and thus calendar system than the global calendar system, i.e. you could have plasmoids on your desktop displaying the Hebrew and Hijri calendars while still keeping Gregorian as your system calendar system. I keep meaning to look at the new plasma calendar widget to see if it supports setting the calendar system, or if I need to add it in.