Ethnologue
The Ethnologue: Languages of the World is a web and print publication of SIL International (formerly known as the Summer Institute of Linguistics), a Christian linguistic service organization which studies lesser-known languages to provide missionaries for their speakers. It contains statistics for 6,809 languages (2000 edition) and gives the number of speakers, location, dialects, linguistic affiliations, availability of the Bible, etc. It is currently the only comprehensive language inventory.What counts as a language depends on socio-linguistic evaluation: see Dialect.
The Ethnologue provides a three-letter code for each language it describes, the number of which significantly exceeds those of ISO 639 and RFC 3066.
