Probleems with slug Backend

Hello, I Have a problem with Slug from Dutch to English. When I’m on an Englisch page and click on a link it doesn’t go to the Englisch link but instead, it goes to 404 page/dutch page with (EN) in the link. someone knows whats going on.

Click on the first link on the page for the problem when you are on the English website.
http://www.svasek.nl/project/olympische-spelen-2016/

tnx

The page I need help with: [log in to see the link]