I've recently read up on the Pirahã tribe and their unique language: apparently it doesn't have recursion. They also don't have words for colours or numbers.

A missionary called Daniel Everett tried to convert them to Christianity but ended up becoming an atheist and linguist.

Conversion certainly didn't go as expected in this case.

This is a nice documentary about them: https://youtu.be/9tKbVBePxyU