Random products in prestashop 1.4

In productcategory.php change:

$categoryProducts = $category->getProducts((int)($cookie->id_lang), 1, 100);

to be

$categoryProducts = $category->getProducts(intval($params['cookie']->id_lang), 1, 100);
if ($categoryProducts) {
shuffle($categoryProducts);
array_splice($categoryProducts, ($nb ? $nb : 10));
}