Columbia subject headings:
Bulgarian language--Variation.
Czech language--Variation.
Language and languages--Variation.
Russian language--Variation.
Slavic languages--Variation.
Sociolinguistics.
Harvard subject headings:
Slavic languages--Social aspects.
Sociolinguistics--Slavic countries.
Princeton subject headings:
Bulgarian language--Variation.
Czech language--Variation.
Language and languages--Variation.
Russian language--Variation.
Sociolinguistics.