As a chemist who had to study German, I note that acetic acid is,
Essigsäure in German and Essig is the German name for vinegar.
Historically, I assume that as vinegar has been around forever, when the
German's started to develop their chemical talents and extracted acetic
acid from vinegar, they naturally called it vinegar acid. Similar
nomenclature evolved for formic acid (Ameisensäure) which is found in
ants (Ameise).