In WP 4 it seems that there is a problem retrieving the categories on a multilingual site. They appear for example only in French or in English. I have to logout and login again to make it work.
I read those articles earlier but I didn’t understand the method to connect mail adresses to selectable recipients. However, when I read this: https://www.agentwp.com/multiple-recipients-dropdown-contact-form-7 I understood. It was really simple and it works fine now. Thanx for this great plugin!