Columbia subject headings:
Harvard subject headings:
Communication--Europe--History.
Communication--Germany--History.
Language and languages--Study and teaching--Europe--History.
Letter writing--Europe--History.
Letter writing--Germany--History.
Pen pals--Europe--History.
Pen pals--Germany--History.
Second language acquisition--History.
Students, Foreign--Europe--Correspondence--History.
Students, Foreign--Germany--Correspondence--History.
Princeton subject headings:
Communication--Europe--History.
Communication--Germany--History.
Language and languages--Study and teaching--Europe--History.
Letter writing--Europe--History.
Letter writing--Germany--History.
Pen pals--Europe--History.
Pen pals--Germany--History.
Second language acquisition--History.
Students, Foreign--Europe--Correspondence--History.
Students, Foreign--Germany--Correspondence--History.