if you turn off the dome lights with the dash switch do they still flash?
do they flash during the daytime or only at night?
the questions are to try and determine if there is a fault or if maybe it was a feature that was programmed to the vehicle, like the horn honk being deleted
if it is a feature that was programmed to the vehicle then you might be stuck or maybe get lucky and find the circuit that makes it happen and hopefully disable it.
another option would be maybe if you have a gm dealer there in Germany you could ask for them to reflash the bcm for Germany, typically a service like that here in the U.S. would be around $100 usd.