Columbia subject headings:
German language--19th century.
German language--20th century.
German language--Variation.
Multilingualism.
Harvard subject headings:
German language--History--19th century.
German language--History--20th century.
German language--Variation.
Multilingualism.
Princeton subject headings:
German language--History--19th century.
German language--History--20th century.
German language--Variation.
Multilingualism.