[bayesian_horse]

When a law requires a government to give permission, it is implied that the decision is not arbitrary, but rather the result of a conscious effort to honor that law.

Requiring permission to prosecute doesn't mean the government can do what it wants in this case. That law is meant to be part of the respect that is given to honest diplomatic partners. At least in the diplomatic fiction, this is the case.

Denying that respect would cast doubt on the numerous treaties between the EU, Germany and Turkey, including NATO membership. Something Germany can ill afford currently.