how many languages exist in the world today
The Cambridge Encyclopedia of Language says that estimates of total living languages in the world vary from 3,000 to 10,000. Voegelins' Classification and Index of the World's Languages (1977) lists 20,000 languages and dialects, grouped into about 4,500 living languages.
There are more than 7000 different languages are spoken by the people around the world today. Anyhow 90% of these languages are used by less than 100,000. You can find more than 7000 dialects in the Ethnologue language dictionary.