See current RFC 5322 ...
http://tools.ietf.org/html/rfc5322#section-3.3
On my computer system (set to Germany and ISO8601) the Mp3tag system variables provide these values:
%_file_create_date% ... 2012-02-15
%_file_create_datetime% ... 2012-02-15 06:29:14
%_file_create_datetime_raw% ... 1329283754
Mp3tag does not support weekday names or month names.
Mp3tag does not provide any function for date time calculations or formatting.
See also ...
/t/8243/1
DD.20120603.1622.CEST