For those who got the same problem as me. I got a webshop with 3 languages. But the German language seems gone, at least the catalog was gone.
Problem? in components/com_oscommerce/includes/jlanguages.php the languages_id was set to 3 instead of 4. Just a reminder if you got the same problem. After changing this setting to the right languages_id the catalog and manufacturers modules show up.