http://dallascao.com/en/2009/07/the-context-sensitive-language-versions-link/

by clicking “中文” at the bottom, he is taken to

http://dallascao.com/cn/2009/07/the-context-sensitive-language-versions-link/

So it involves replacing the “/en/” the URL of the current page with “/cn/”.

The following php code gives out wrong results:

<?php $url_old = "http://".$_SERVER ['HTTP_HOST'].$_SERVER['PHP_SELF']; ?>
<?php $url_new=str_replace("en","cn",$url_old); ?>   
<a href=<?php echo $url_new; ?>Chinese</a>

Whichever page you are visiting, $url_old always gives the home URL “/en/index.php”. This is because I turned Permalinks on and the URL is rewritten. The URL rewritting takes place after the execution of PHP codes on the server side, and therefore the php string “$url_old” cannot get the actual URL as it is rewritten afterwards. The following java script can get the right current URL as java script runs on the client’s computer:

<script>
var s=window.location.href
r=s.replace (/en/, "cn");
document.write ("<li><a title='English verion of this page' href="+r+">Chinese</a></li>")
</script>

More information:

java replace () method