I'm doing some run research/reading on different languages of the world (in celebration of PM now having for sale the French, Spanish and Arabic translations of The Peacemaker), and I came across an ethnologue.com webpage on the linguistic diversity of countries.
The #1 linguistically diverse country? Papua New Guinea (no wonder I hear about all these Wycliffe workers there!) -- there are 820 living languages in PNG, and if you were to pick two people at random, the odds of them speaking different languages are 99%.
The #2 country? Vanuatu. WOW, if you're like me, you gotta learn lots of new things every day, and you've never heard of Vanuatu. Turns out it's an island nation in the South Pacific, with 97.2% linguistic diversity.
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According to the CIA World Factbook, "Multiple waves of colonizers, each speaking a distinct language, migrated to the New Hebrides in the millennia preceding European exploration in the 18th century. This settlement pattern accounts for the complex linguistic diversity found on the archipelago to this day. The British and French, who settled the New Hebrides in the 19th century, agreed in 1906 to an Anglo-French Condominium, which administered the islands until independence in 1980, when the new name of Vanuatu was adopted."