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.
A law is only a law as long as it can be enforced by courts and agencies. That's what jurisdiction means. And it's not "my definition", it's Cornell Law Schools.
"Your definition" in the meaning of "the definition you cite".
If you read the page you linked closely (and remove all the US specific stuff) you see that it really only talks about of enforcement not lawmaking. Your own addition
> Jurisdiction is what allows the government to make a law in the first place
can nowhere be found on the page you linked.
There are a lot of laws in the books everywhere in the world that are usually not enforced because you can't. Germany (as well as many other countries) has laws regarding human trafficking that apply to anyone everywhere in the world. Would you argue that this is not a law? If that's the case we can agree to disagree.
I know that declaring a definition to be wrong is quite a stretch, but I think a more agreeable definition of what is a law depends of the corresponding jurisdiction. In Germany, certain rules made in a process by the Bundestag are, by definition of the constitution, a Gesetz, and ’Gesetz’ is the german word for ’law’. So, these laws wouldn’t necessarily be laws following your definition, which makes your definition unacceptable, I’d say.
What you are calling ’law’ I would maybe call ’enforced law’ or ’enforcable law’(by whom?). Well, whether the rules in question are of this kind is what will be found out in court.
The only problem would be enforcing the law. As Facebook has offices in Germany and targets German customers that shouldn't be too hard.