Thank you for your message.
That error message occurs when you try to delete a culture from a website when it has pages in this culture. The only way to remove the Czech and Dutch culture would be to delete the pages in this culture. This does not involve deleting the actual page for all cultures, only that of these cultures. To accomplish this, just go into the specified culture you're wanting to delete and try and delete each page that has been created for it. As long as you do not check the box next to "Delete all culture versions of the specified document", the document will only be deleted in this culture. So only after you go through and delete all the pages for these cultures you no longer want will you be able to remove the cultures from your site.
Junior Support Engineer