It's not actually true that Germany bans RT. What is true is that German media regulators have ruled that RT can only be broadcast in Germany if it is accompanied by a disclaimer noting that it is a Kremlin-funded channel. This rule was put in place after it was revealed that the Russian government had been using RT as a propaganda tool to influence German public opinion. France24 and Voice of America are not funded by the Russian government, so they don't need to be accompanied by disclaimers in Germany.