is it somehow possible to assign two (or more) differenct keyboard shortcuts to the same action?
Specifically I want 'Alt+Tab' _and_ 'meta+j' to toggle through windows.

Depends on if this is for Global shortcuts or general shortcuts. For Global shortcuts, the user interface currently restricts you to a single shortcut and it is not possible to set multiple shortcuts.

As a workaround, you could use Xmodmap to map the second combination to the first, which would cause KDE to see the second combination as if it were the first, triggering the action.

I'm not sure if there is a technical limitation in the shortcuts infrastructure or if it is a purely user interface limitation though.

Thanks for taking the time to answer!

bcooksley wrote:Depends on if this is for Global shortcuts or general shortcuts.

What is the difference between a Global shortcut and a general shortcut?

bcooksley wrote:As a workaround, you could use Xmodmap to map the second combination to the first, which would cause KDE to see the second combination as if it were the first, triggering the action..

I had a first look at xmodmap. It seems to me that one can only map single keys and in order to bind my whole combination I would have to bind Alt to Meta and Tab to J. Or is my impression completely wrong?

A global shortcut applies everywhere - even when the application does not have focus (the volume keys and KMix being a notable example).
A general shortcut only applies in that particular application, and will not work when it is not focused (Ctrl + P in Okular for instance).

With regards to xmodmap - damn. You could try using the Custom Shortcuts support in KDE, configurable in System Settings with the alternate key press and use something similar to http://bharathi.posterous.com/x11-fake- ... -xtest-ext to simulate the first key combination.