Had you asked me a few months ago about what language they speak in Argentina, I probably would have just said Spanish, assuming (erroneously of course) that all spanish speaking countries all speak the same form. Now that I'm here, I know what a lot of people in North American probably don't - in Argentina they speak a fairly different form of spanish based on Voseo, and also have some very unique pronunciations. The main change in voseo that the second person singular (equivalent to you in english, i.e. you are) is changed from tu to vos. Unfortunately very few books even make mention of this ...