It seems the system settings accessible through the kUbuntu GUI does not suffice to change the default system language, or at least it is not as intuitive as it should be. As this is the language used at the login screen and especially in the Konsole, it can be horribly annoying.
You can check your locale setting using
% locale
To fix it the hard way, just edit
/etc/default/locale
to you liking or use
update-locale
and reboot.
