if (!empty($_GET['language']))
$_COOKIE['language'] = $_GET['language'];
else
$_COOKIE['language'] = 'en';
setcookie('language', $_COOKIE['language']);
if ($_COOKIE['language'] == "en") {
$textdir = "ltr";
}
else if ($_COOKIE['language'] == "he") {
$textdir = "rtl";
}
<!doctype html>
<html lang="<?php echo $_COOKIE['language']; ?>" dir="<?php echo $textdir; ?>">
<head>
...
</head>
<body>
<a href="index.php?language=en">English</a>
<a href="index.php?language=he">Hebrew</a>
</body>
</html>