German or Mandarin or both?

Hello, I'm an automation engineering student who's interested in languages. In my country it's mandatory to learn 3 languages up to highschool (more if you're in a languages branch. The main three are Arabic, french and English) + we speak a dialect as a main language. I'm interested in learning more languages like japanese, korean, spanish, portuguese, russian, extra, but professionally, which language is more useful for my field?