Created attachment 2029 [details] Screenshot Wrong layout size at window "Edit contact details". See screenshot.
Ok, but could it pend on font size? Language?
Yes. Can you resize the window?
Yes, new issue title is correct: default size (height) is just too small. It becomes OK if I increase the height. BTW, also note: a blank space below "Ok" and "Cancel" buttons.
Similar for "View -> Go To... -> Folder (G)" dialog (small width issue, see "Screenshot 2.png").
Created attachment 2059 [details] Screenshot 2
Similar for "Move...", "Copy..." message's context menu's dialogs (see screenshot 3).
Created attachment 2067 [details] Screenshot 3
The default height is unset. Your problem is probably caused by first running gtk2 claws-mail, where your height was set, and then running gtk3 claws-mail, which used the height preference saved previously. Gtk3 wants more space than gtk2, thus it looked too small.