Detecting a user's URL

$currentUrl = "http://" . $_SERVER['HTTP_HOST']  . $_SERVER['REQUEST_URI'];

if (strpos($currentUrl, "en") != FALSE) {
    // user is english...
    echo "Hello";
} else if (strpos($currentUrl, "fr") != FALSE) {
    // user is french...
    echo "Bienvenue";
}
// you can keep adding else-if statements for other languages