Translation not showing all on fornt-page

I have a site, front-end, back-end & content all set to Dutch language, I also copied the translation file.
But not all is showing in the front-end as Dutch.
Some text are, some not. The form fields First name,... aren't in Dutch,
In the back-end when I go to translations, I see the correct Dutch translation.

site: www.51-aarschot.be

Hi

For these fields on form, please go to Events Booking -> Custom Fields, edit the custom fields and change title of these fields to your language. After that, it will work as expected

Tuan