Problem:
I translated the site succesfully. The only part which did not translate properly is the Mollie form
Solution:
To fix it, I went to WPML -> Settings -> Post Types Translation > Mollie Forms (mollie-forms) and marked it as 'Translatable (use translation if available or fallback to default language)'.
Now if I go to 'Mollie Forms' I can see the Donation form in there and it is possible to add a translation for it.
