Thanks Ron.
After your reply I started using Multi Language Switcher. (https://wordpress.org/plugins/multisite-language-switcher/) and put every language in their own subdir (denhaag.domain.com for Dutch and thehague.domain.com for English).
And I've decided it would just be easier to drop WPML all together. This works much easier in my case than coping with WMPL. Also because I am using EM Pro as well for event bookings and that just doesn't play nice with WPML.
But thank you very much, Ron! Without your reply I would've never found the Multisite Language Switcher. :-)