Our addition of "er" comes from the German language.
Someone or something from Hamburg, Frankfurt or Lich for instance, would be called a Hamburger, Frankfurter or Licher
For instance Pilsner is a type of pale lager. It takes its name from the Bohemian city of Plzen (German: Pilsen), where the world's first pale lager was produced in 1842 ...
A one time favorite of mine...
and they're actually owned by the Bitburger Group.