Your definition only refers to government agencies and courts. Not the body creating the laws in first place. The German parliaments are free to create any law

Your definition only refers to government agencies and courts. Not the body creating the laws in first place. The German parliaments are free to create any law they like (as long as they respect the German constitution). The only problem would be enforcing the law. As Facebook has offices in Germany and targets German customers that shouldn't be too hard.