As an update/additional info: technically it works perfect.
Technically, the URL-slugs do include the '/en/' or '/nl/'
Because when you click the EXAMPLE ERROR URL you get a 404 page.
If you then manually add either '/en/' or '/nl/' in the URL, the correct page loads.
So, it must be some template coding, but I have trouble finding the exact location to fix it.
Basically this string is returning the wrong value: tribe_get_events_link()