Thanks for the very quick reply.
Most of the problems are solved right now.
1. When I want to change languages a couple of times, the URL got stuck like this: http://www.autoradioexpert.nl/de/it
(the "de" stays and "it" comes after)
2. The buttons, input fields are in the hikashop webshop, I can't change it I think? Do you know how this works?
3. At the moment I can't effort a enterprise version. Is there no other way to solve this?
I will write a good review on joomla, very satisfied !