Like incorrect grammar in any language although Germans seem a little more sensitive. Lots of nuance and situational stuff...declension, gender etc. (We have only one “the”!)
2 years in high school and one year in college. Stationed in WesT Berlin in ‘60’s. Maintained a basically C level of proficiency for the Air Force. Been many years since those days.
Must have been a great experience at Universität Trier!
Stunning place.