Formatting dates according to the region

[Dylan McCall <dylanmccall gmail com>]

GNOME Control Center's Region & Language panel lists four different
date formats for the selected region. For Canada, for example, it
lists:

Monday 16 April 2012
16 April 2012
16 Apr 2012
12-04-16

However, g_date_time_format(datetime, "%x") only returns a date
formatted in that last way. How can an application use other date
formats for the current region? Preferably without duplicating code,
or, at least, effort.