Change language at runtime

Hi there,

I was wondering if anyone could help me.. I created a small site and it has 2 languages.. To devide the posts, I simply give them a different language-category…

To determine which images to put I simply do a check, for example:
” <?php if (in_category(‘fr’)) { ?>”. You get the idea..

Now, that leaves me with one problem.. I’d like to switch the wordpress language on runtime also.. but I can’t seem to find how?
Is it possible at all?

I’d like to somehow do it when the page is being loaded:
Something like:
<?php if (in_category(‘fr’)) {
define(‘WPLANG’, ‘fr_FR’);
?>

Any help would be much appreciated!

thanks in advance,

Ben