Dance is not a language. Rather, it is a form of expression, and can be a very powerful one at that. Language must be structured and consistent, it has set meanings and definitions of its words. Dance, has no structured means of communication, rather, it is dependent on interpretation by the audience. In language, ideas are communicated through expression of words, as opposed to dance, in which ideas are communicated through expression of movement, which itself is subject to interpretation.
People in a movement often try and elevate their cause through elevation of diction (there was an article in the new york times recently how the word ‘curate’ now applies not only to those who work in museums, but to anybody who puts effort into selecting something artistic: http://www.nytimes.com/2009/10/04/fashion/04curate.html?_r=1&pagewanted=1). But this shouldn’t be the case with dance. To make dance a language would take away the interpretive nature of it. It would make the message of the artist completely supersede the experience of the viewer. There is already a name for language through movement: sign language. Characterizing dance as language instead of expression not only fails to elevate it, it demeans it.