Columbia subject headings:
Harvard subject headings:
German language--Study and teaching--Foreign speakers--Bibliography.
German language--Study and teaching--Portugal--Bibliography.
German language--Study and teaching--Spain--Bibliography.
German language--Textbooks for foreign speakers--Bibliography.
Second language acquisition--Bibliography.
Princeton subject headings:
German language--Study and teaching--Foreign speakers--Bibliography.
German language--Study and teaching--Portugal--Bibliography.
German language--Study and teaching--Spain--Bibliography.
German language--Textbooks for foreign speakers--Bibliography.
Second language acquisition--Bibliography.