As explained in this Stern article, Brazil's Pirahã tribe have one of the most unusual languages on earth:
"The language is incredibly spare. The Pirahã use only three pronouns. They hardly use any words associated with time and past tense verb conjugations don't exist. Apparently colors aren't very important to the Pirahãs, either -- they don't describe any of them in their language. But of all the curiosities, the one that bugs linguists the most is that Pirahã is likely the only language in the world that doesn't use subordinate clauses. Instead of saying, "When I have finished eating, I would like to speak with you," the Pirahãs say, "I finish eating, I speak with you." Equally perplexing: In their everyday lives, the Pirahãs appear to have no need for numbers."