German law isn't my strong point, but EU concordats with respect to regulatory bodies means harmonisation of aspects of professional ethics, conduct and obligations.

I am a doctor, I am on the specialist register with The General Medical Council and could in theory practice under German law, as local registration is a quick process within EU states where you are already registered.

With regard to mental health, an example was given above of psychiatrists informing DVLA. Where a psychiatrist is involved in care, the patient would come under either The Mental Health Act 1983 where decisions are made for the patient by others or The Mental Capacity Act 2005 where the decision to disclose to DVLA was made in the best interest of the patient, as the patient lacked the capacity to be trusted to inform. In any case, and not just mental health but any aspect of health, a health care professional has the duty to disclose in the public interest where they have advised a patient of the patient's obligation to disclose and have grounds for concern that this would not happen, coupled with public safety risks if nothing is done. This is dealt with under The Health Act 2006 and a regulatory clause under The Health and Social Care Act 2008 regarding taking national guidelines into account when assessing and delivering care.

Again, having read a number of articles over this case, and it is of huge interest to our profession, should precedents follow, I am still not clear regarding detail. What is clear however is the wish of the OP to use this tragic episode for a sick crusade against human rights.