The formats vary with the user's language.
Options are made available for a language if listed in the
$datePreferences array of its messages file (
The ID used in the list needs to be named in the
$dateFormats array (whether the general one or the override in the
Messages*.php file in question) and defined there with the appropriate
sprintfDate() format; otherwise it will be ignored.
The options are then listed in Special:Preferences accordingly to the definitions, in the same order. They use January 15, 2001 as example. For English they are:
- default (No preference)
- mdy (16:12, January 15, 2001)
- dmy (16:12, 15 January 2001)
- ymd (16:12, 2001 January 15)
- numerical yyyy-mm-dd (like ISO 8601, but without calendar conversions, and without implying that it is the date according to the Gregorian calendar)