Columbia subject headings:
Harvard subject headings:
Classification
German language--Dialects--Germany--Frankfurt am Main.
German language--Phonetics
German language--Phonology
German language--Phonology, Historical.
German language--Vowels.
Princeton subject headings:
Classification.
German language--Dialects--Germany--Frankfurt am Main.
German language--Phonetics.
German language--Phonology, Historical.
German language--Phonology.
German language--Vowels.