Not sure where a particular language is spoken? Try this (free!) great map by Stephen Huffman. The pdf-file is downloadable and searchable!
Unfortunately, there’s only one name per language, which means that the particular name you’re looking for may not be there. If not, try one of the alternative names for the language,
e.g. if you’re looking for “Belhare” but don’t find it (you won’t), try “Belhariya”.
And of course, to get more general information on virtually any language anywhere, there’s probably no better starting point than the Ethnologue!