Updating a GET variable

Hi folks, I'm sure this is an easy one that's standing right in front of me but I'm too blind to see. I have a page with an URL like this: index.php?name=value&this=that. I have a link on the bottom of the page which allows the user to switch languages. I need to hang onto the existing $name and $this get variables. I tried <a href='&lang=en'>Flip</a> and it loses all previous GET data. Then I tried <a href='<?php echo $_SERVER['SCRIPT_NAME'] ;?>?<?php echo $_SERVER['QUERY_STRING']; ?>&lang=en'>Flip</a> And it continually appends more &lang=en's to the URL if the user keeps clicking on it (for whatever reason). Now I've put it in a form and it works as expected, but the display value and my under-the-hood value need to be different, so it's a fail. What's the best way to update the value of a GET var? Marc