Ah! The labeling on that first diagram makes sense now.
As for the second, it appears to be a regular 3-way switching arrangement but with double-pole switching and thus four travelers.
It took me a while to figure out why anyone would need to do this, but I think I have an explanation.
Don't parts of Norway use a 220V IT system (i.e. neither pole is grounded) ?
Wiring a 3-way light this way would insure that when the switches are set for the light to be off that both poles on the lampholder are disconnected from the supply.
