Thread:Project:Support desk/Change Default Calender Style/reply (7)

Have a look at your user preferences, check the source code of that page and there search for "mw-input-wpdate-ISO_8601". That is the place, where the ISO 8601 option is defined. Somewhere near there should also be the date format you want. You will see that in the source code, there are several ids defined. I think what you need to know is the part of that id, which follows after the mw-input-wpdate-; that is what I would try setting as value.