Unfortunately Kubuntu does not install the required packages to enable proper application-wide spell-checking. Here is a guide to enable auto spell-checking for all applications in Kubuntu.
1. Install the required packages ($lang is your language shortcut, e.g. en or de):
sudo apt-get install kde-l10-$lang language-pack-kde-$lang aspell-$lang hunspell-$lang
2. Setup and enable auto spell-checking in KDE:
Open the KDE system settings and go to
Locale
There select
Spell Checker and enable
Automatic spell checking enabled by default and check your default language (in this case
German (Germany)). If you finished set confirm with
Apply.
In some applications spell-checking is now enabled by default, like
LibreOffice Writer in other you have to enable it, like
KMail (New Message -> Right-Click).
Enjoy !