http://en.wikipedia.org/wiki/Flesch%E2%80%93Kincaid_readabil...
A brief search on wikipedia reveals a few readability tests, but they all seem to be based on sentence/syllable ratios, not content complexity.
http://en.wikipedia.org/wiki/Category:Readability_tests
And in general they all rank multi-syllable (longer) words higher. Which would mean a conversation between two Java API writers would be ranked higher than a ruby conversation :)
Java vs Ruby vs Lisp: http://i.imgur.com/tq3pA.png