I want to build an external indicator for my current keyboard layout; basically, a DigiSpark (http://digistump.com/category/1) with an RGB LED. I already know how to talk to the indicator (it's a raw USB device, just use libusb!), but I don't know how to get access to the keyboard layout state.

What is the proper way of doing this? Listen to the DBUS for keyboard change messages and act accordingly? Where is this documented? Or find the source code for the keyboard layout indicator (again, where is it?) and hack that?

qdbus org.kde.keyboard /Layouts