Menu callback; Retrieve a JSON object containing a suggested time zone name.
function system_timezone($abbreviation = '', $offset = -1, $is_daylight_saving_time = NULL) {
// An abbreviation of "0" passed in the callback arguments should be
// interpreted as the empty string.
$abbreviation = $abbreviation ? $abbreviation : '';
$timezone = timezone_name_from_abbr($abbreviation, intval($offset), $is_daylight_saving_time);
return new JsonResponse($timezone);
}