hi @tristup,
Was afraid this was going to be your reply 
Can you tell me what the difference is between:
Header > Assignment > Conditions > First Page: Is being viewed
and
Header > Assignment > Conditions > Front Page: Is being viewed
I’ve made two different headers now, Dutch and English.
I’ve set the Dutch: Header > Assignment > Conditions > Front Page: Is being viewed
and the English: Header > Assignment > Conditions > First Page: Is being viewed
I want the Dutch menu appear only on pages in Dutch
and vice versa; English menu for pages in English
So far it seems to work, but not sure really why it works 
Thanks!
ps. if you want to look at it, the credentials are still the same as mentioned above in the secure note