If you create change or an Contact via CardDav The encoding gets mangeled.
(UTF-8 interpreted as iso-8859-1 ?)
If you change the contact in the Kopano Webgui the carracters arrive corrrectly at the CardDav clients.

Tested with:
Thunderbid + CardBook
Win10

Examples:
Expected
ÄÜÖ -> Ã�Ã�Ã�
Comércio -> Comércio