Germany restricts insulting individuals / your neighbour, police officer, a pastor or a minister. There’s no special law for politicians. Political criticism is protected under the Basic Law (constitution). Go ahead and be crucial about a politician’s actions but don’t insult their person’s honour or use a slur. That’s not your freedom of speech, that’s the dignity. In fact, you can even insult the government! You can say German government as the government is not a person.