You can add any you want with the following config options:
// use this format for date display (date or strftime format)
$config['date_format'] = 'Y-m-d';
// give this choice of date formats to the user to select from
// Note: do not use ambiguous formats like m/d/Y
$config['date_formats'] = array('Y-m-d', 'Y/m/d', 'Y.m.d', 'd-m-Y', 'd/m/Y', 'd.m.Y', 'j.n.Y');