Language and Thought

Here's a good article about the cognitive effects and benefits of language.

Lupyan found that participants who were given names for the aliens learned to identify the predators far more quickly, reaching 80 per cent accuracy in less than half the time taken by those not told the names. By the end of the test, those told the names could correctly categorise 88 per cent of aliens, compared to just 80 per cent for the rest (Psychological Science, vol 18, p 1077). So naming objects helps us categorise and memorise them, Lupyan concluded.

However language emerged, it seems that our inner voice changes the way we experience the world. "Language is like augmented reality - an overlay that changes how we think, reason and see," says Clark. Boroditsky believes that this is as relevant to us today as it was to early humans. "The sheer amount of information arriving down the optic nerve is far more than the brain can process consciously," she says. Language, she believes, is how the human brain focuses on the essential details. "It's like a guidebook that has been developed by thousands of people before you, who have figured out what is important for us to survive and adapt to our environment." 

This has important and ominous implications that are not discussed in the article.  If language is so important to thought, then people with smaller vocabularies will, ceteris paribus, be worse at thinking, and on a very fundamental level.  They experience the world differently than those with rich vocabularies; their world will be full of confusing, complicated, and unclassifiable objects and concepts.  This is a horrifying handicap to a successful life.