Use case

There are many calendar systems besides for common Gregorian. For example, there is the Jewish Calendar, which is a lunar calendar, but extra months are added (according to a fixed mathematical system) to make it more or less end up matching the solar calendar.

I would like to allow users to select a date on the Jewish calendar, which is easier for users because the holidays are according to that calendar.

It would be great if the date picker wasn't hard coded to use gregorian, and could be configured to use other calendar systems.

Proposal

I am by no means a calendar expert. For inspiration, angular material date picker has been calendar agnostic for some time now.

In C#, the one and only John Skeet supports many calendars in noda time

Perhaps is this something which should be handled in dart first?

This looks like a good rundown of how the Jewish calendar is calculated, but really my intent with this issue is more about the general methods by which support could be added for any calendar system, not so much that support for a particular calendar system be added (although that would be great!)