I have 2 calandars, one in English en on in Dutch. Everything is in dutch, outlook (webbased and APP) but I have 2 default calandars named Agenda(dutch) and Calandar (English). The same on Contacts(English) and contacten(Dutch).
How can I remove the english version so that I have one Calandar (Dutch) and one contacts (Dutch)
If the Dutch ones are the default folders, then you should have no problem deleting the English ones.
If you can't remove the English ones but only the Dutch ones, then move over any content from those folders into the English ones, remove the Dutch folders and then restart Outlook with the /resetfoldernames switch.