To display only one language you must replace with
$category_query = "SELECT DISTINCT `categories_description`.`categories_name`,`categories_description`.`categories_id`,`categories`.`parent_id` FROM `categories_description`INNER JOIN `categories` ON (`categories_description`.`categories_id` = `categories`.`categories_id`) WHERE (`categories_description`.`language_id` = 1) ORDER BY `categories_id` ";
$product_query = "SELECT DISTINCT `products`.`products_id`,`products`.`products_quantity`,`products`.`products_model`,`products`.`products_image`,`products`.`products_price`,`products`.`products_date_added`,`products`.`products_last_modified`,`products`.`products_date_available`,`products`.`products_weight`,`products`.`products_status`,`products`.`manufacturers_id`,`products_description`.`products_name`,`products_description`.`products_url`,`categories_description`.`categories_name`,`products_description`.`language_id`,`manufacturers`.`manufacturers_name` FROM `products` INNER JOIN `products_description` ON (`products`.`products_id` = `products_description`.`products_id`) INNER JOIN `products_to_categories` ON (`products_description`.`products_id` = `products_to_categories`.`products_id`) INNER JOIN `categories_description` ON (`products_to_categories`.`categories_id` = `categories_description`.`categories_id`) INNER JOIN `manufacturers` ON (`products`.`manufacturers_id` = `manufacturers`.`manufacturers_id`)
WHERE (`products_description`.`language_id` = 1) AND (`categories_description`.`language_id` = 1) AND (`products_to_categories`.`categories_id` = " . $row['categories_id'] . ")";
i have choosen lanuage_id=1 if you have other you can put e.g. lanuage_id=4