I'm about to finish my postdoc employment and looking for a job in the industry (both in Germany). I know that a typical thing to add to the job applications for the industry is the "employment reference letter" (it is Arbeitszeugnis in Germany). However, I'm not sure if they expect such a thing from people who come from academic positions? Also, if I ask my group's head for such a letter, would it sound uncommon?
Yes, you should ask for one and your professor should know what it is and how to write one. That said, some professors haven't been in Germany long enough to have experience with this, and others are just too busy for formalities. So what often happens is they will tell you to write your own and they'll sign it, or they'll tell you to ask the HR department to write one.