It's funny how you created a scenario of an upstanding family man (German, so probably white), obviously highly educated, and has a kick *** job. You didn't say if he entered illegally. He's gonna be here at least 4 years. Is that possible? How long do visas go for. IDK. Using your logic, since he is paying taxes he should be able to vote locally. Why not State or Federal? How does one say you can do one, but not the other. That would be the next logical step, no?
Lets reverse things. Name me a country that I can move to, live in for 4 years, NOT become a citizen, and vote in ANY type of that countries election.