A useful book and website on languages. It is published by the Summer Institute of Linguistics (SIL), a group whose purpose is to create Bible translations; but unlike most such missionary groups, they are serious about linguistics, and their monographs on obscure languages from all over the world are absolutely invaluable.

I haven't seen the book, but I refer to the website a lot: it's at

It's not a linguistics text: you won't find any explanations of anything, even of why they classify languages as they do, but what they do well is classify them. (It doesn't mean they're right: opinions often differ, and to get it in their list they often have to pick one position and stick to it.)

Every single language, language name, dialect, family, is recorded in many spellings and synonyms: you can look up by country, continent, family, or name. Then they encode them into a three-character code, and refer you to an entry for a country.

This entry lists dialect names, number of speakers, precise location, the chain of family and subfamily classification that they've assigned it to, the percentage of literacy, the status of the written language, and as a very brief unobtrusive note the existence of Bible texts.

As an example, English has 83 different entries, for the 83 different countries in the world it's spoken in. So here is the entry for English (United Kingdom). For clarity I haven't hardlinked it: the links in there are those that occur in the website.

ENGLISH [ENG] 55,000,000 first language speakers in United Kingdom (1984 estimate); 322,000,000 in all countries, first language speakers (1995 WA); 470,000,000 including second language speakers (1995 WA). Also in USA, Canada, other former colonies, many countries. Indo-European, Germanic, West, North Sea, English. Dialects: COCKNEY, SCOUSE, GEORDIE, WEST COUNTRY, EAST ANGLIA, BIRMINGHAM, SOUTH WALES, EDINBURGH, BELFAST, CORNWALL, CUMBERLAND, CENTRAL CUMBERLAND, DEVONSHIRE, EAST DEVONSHIRE, DORSET, DURHAM, BOLTON LANCASHIRE, NORTH LANCASHIRE, RADCLIFFE LANCASHIRE, NORTHUMBERLAND, NORFOLK, NEWCASTLE NORTHUMBERLAND, TYNESIDE NORTHUMBERLAND, LOWLAND SCOTTISH, SOMERSET, SUSSEX, WESTMORLAND, NORTH WILTSHIRE, CRAVEN YORKSHIRE, NORTH YORKSHIRE, SHEFFIELD YORKSHIRE, WEST YORKSHIRE. 60% lexical similarity with German, 27% with French, 24% with Russian. National language. Typology: SVO. Christian. Braille Bible. Bible 1382-1989. NT 1380-1995. Bible portions 1530-1995.
For comparison here is the entry for the United States. of course the UK has the bulk of dialect differences in English, but it is striking that they mention only one dialect here. As I suggested, have your pinch of salt ready. The Ethnologue listing is excellent for what it is, but it's not gospel.
ENGLISH [ENG] 210,000,000 first language speakers in USA (1984 estimate); 322,000,000 first language speakers in all countries (1995 WA). 8,400,000 USA residents with no one 14 or older in their family who speaks fluent English, or 38% of 7,700,000 households headed by immigrants. Over half speak Spanish, 18% an Asian language, 28% mainly a European language (1993 USA Census Bureau). Indo-European, Germanic, West, North Sea, English. Dialect: BLACK ENGLISH. National language. Braille Bible. Bible 1382-1989. NT 1380-1993. Bible portions 1530-1993.
Compare Australia:
ENGLISH [ENG] 15,682,000 in Australia (1987), 95% of population (1980 WA); 322,000,000 in all countries (1995 WA). Indo-European, Germanic, West, North Sea, English. Dialects: AUSTRALIAN STANDARD ENGLISH, ABORIGINAL ENGLISH, NEO-NYUNGAR (NOONGA, NOONGAR, NOOGAR). Minor regional dialect differences. Dictionary in Noongar. National language. Braille Bible. Bible 1382-1989. NT 1380-1993. Bible portions 1530-1993.