The configuration dialog crashes after selecting VPN type on my locale
(see below). After checking ~/.xsession-errors it looked like it was a
problem with the locale I use (see below). I changed the locale using
dpkg-reconfigure locales, and changed it to en_GB.UTF8, and rebooted.
When I then tried to configure the VPN again, it didn't crash.
I changed it back to de_de (== .iso-8859-1) and it crashed the configuration:

Relevant part of the log:
=== BEGIN LOG ===
(nm-connection-editor:3661): Gtk-WARNING **: Failed to set text from markup due
to error parsing markup: Fehler in Zeile 2, Zeichen 33: Ungültiger UTF-8-kodiert
er Text im Namen - »Nur mit Servern verbinden, deren Zertifikat den angegebenen
Betreff enth\xe4lt.
Beispiel: /CN=myvpn.company.com« ist nicht gültig
===