function for returning a formatted date with an optional interval
function formatDate($dato, $interval = NULL) {
$format = isset($_SESSION['pagelang']) && $_SESSION['pagelang'] == 'en-GB' ? 'Y-m-d' : 'd.m-Y';
if(!empty($interval)) {
$date = date($format, strtotime("$dato +$interval days"));
} else {
$date = date($format, strtotime($dato));
}
return $date;
}