help with sessions

Hi all.

I have a problem that has been doing my head in for quite a few hours and hope that someone can help, any help would be very much appreciated.

I have a referral system on my members site and want to include a language choice which i have accomplished.

The problem is if a person goes to the site url:

mysite.biz/15/index.php?referid=Pab ...

Then clicks on a language - say he chooses dutch the page goes to:

mysite.biz/15/index.php?ln=nl

and drops the ?referid=pablo

how do i change the following session to include the referid also.

<?php

session_start();
error_reporting(E_ALL);

include("../language/Language.php");
if(isset($_GET['ln'])) $_SESSION['language'] = $_GET['ln'];
Language::Set($_SESSION['language']);
Language::SetAuto(true);

?>

Thanks for looking and thanks in advance of any help.

Paul.