Kubuntu 16.04 Plasma can not start after fresh install

The problem seems to be that the Dutch translations (kde-l10n-nl) of KDE conflict with plasma-desktop. Forcing the reinstallation of plasma-desktop in a TTY fixed the issue. You don't have to reinstall kubuntu-desktop for this to work:

apt-get install --reinstall plasma-desktop 
apt-get -f install 

Some packages that are needed for KDE to run are missing or misconfigured.

Enter a TTY (Ctrl + Alt + F1) and log in there. Run sudo apt-get install --reinstall kubuntu-desktop kde-* || sudo apt-get install -f and KDE should start.

You'll have to be connected to the internet for this to work.

Actually, I had the same problem and it is related to the cached content. Just go down to the console with Ctrl + Alt + f1, log in, and:

~$ cd ~/.cache
~/.cache$ rm -rf *plasma* *kde*

exit - change back to the UI with: Alt + f7 (Usually) and log in through sddm again. Should work now.

The first login will take longer than usual - as it needs to rebuild all the caches. But apart from that - it's working.

Make sure you really log out out of GUI ! If not it won't really work.