*flicks tail in annoyance*
I think that humans actually can understand cat language (comprehend it, however, is a different story), it's just that we can't really communicate to them in it.
For instance, I know how to recognize certain meows that my cat makes (He makes one sound for lonely, one sound for when he's about to barf, one sound as a greeting, one sound to mean he wants to be fed, and one sound when he wants to be petted - unfortunately, the last one is nearly identical to the "wants to be fed" one) but sometimes it's like he's trying to converse with me and I have no idea what he's trying to communicate.