Dates are always represented in year-month-day format here. This is just as true of one's date of birth, which is referred to by the word 生年月日 (sei-nen-gappi, lit. "birth year month date"). When you put this word on a form, you are asking people to enter the information in that order. And no, there's no such thing as a sei-gappi-nen.
... Well, it's funnier in Japanese.
I would really appreciate seeing an option to display the form in the proper order. I can think of two ways to do it. The really slick way would be to have the program parse the date format specified in the language and present the options in that order. But that would take a lot of work, and handling all the possible errors would probably be a drag.
So the best option is probably a bit more prosaic: add a DOB format selector somewhere in the ACP - Options - Registration page, with radio buttons to select between them. The selector should be capable of accommodating additional formats as necessary.
Here are my preferences for a Japanese language setting: we don't really need a drop-down list for the month, because months are numbered here. Instead I'd like to see three text boxes with a phrase displayed after each, as follows:
[................ ] 年 [........ ] 月 [........ ] 日
The "year" and "day" phrases can be used as-is for this. A "month" phrase would need to be added after the second text box. (Why not put the phrases in the text boxes, you say? Because they disappear when you enter numbers. If they stay visible in the order shown above, the result is a properly-written Japanese date.)
This change is fairly essential for any Japanese site. I suspect it would be useful for Chinese sites as well; and other regions may benefit from the general idea of a DOB format selector.
Respectfully submitted for your consideration. m(-_-)m