@hellpie @0xabad1dea Japanese date format is almost certainly something that they have a solution for-you *could* just indicate the difference in the U.I., but store the date format the same way internally.
That,and you can test it on any given day much easier.Leap years you have to check for specific years it's being set for (Generally) every four years, that sounds like the easy check...except for the exceptions when within 4 years it's not a leap year.
It's a harder version of DST checking...