The ability to communicate is another important aspect of intelligence which cannot be overlooked. The problem here, however is that one cannot rely solely on this as a measure of intelligence. And yet, one still felt, he was of normal intelligence, despite these manifest limitations of intellectual functioning. If you look at this example closely, you will notice that Joseph had all of those abilities and merely needed the language to develop and express them. In this sense, I would argue that language is not a prerequisite of intelligence but a facilitator.
Language does, however, have one interesting factor that demonstrates intelligence.
It demonstrates brainstorming. An excellent example that Calvin points out is language. For example, the words dog, retreiver, and poodle, are all related. The same can be said for the words bit, bite, chew, and eat. Finally, mailman, postal worker, postal courier, and other such words have a strong relationship.