- en.php
$expira = time()+60*60*24*30;
setcookie("lang", "en", $expira);
$voltar = $_SERVER['HTTP_REFERER'];

header('Location: ' . $voltar);

- pt.php
$expira = time()+60*60*24*30;
setcookie("lang", "pt", $expira);
$voltar = $_SERVER['HTTP_REFERER'];

header('Location: ' . $voltar);