PHP Multi-Language

lang-en.php
<?php
 define( "WELCOME", "Hello " );
 define( "DAY", ", we wish you a nice day." );
?>

lang-ro.php
<?php
 define( "WELCOME", "Salut " );
 define( "DAY", ", iti dorim o zi placuta." );
?>

<?php
require_once( "/lang-$_SESSION[lang]" );
?>

<div><? echo "WELCOME" . $login . "DAY" ?></div>
<!-- this should output, for English, : 
Hello John, we wish you a nice day. -->