While,
theoretically, music is not an universal language, it
practically may as well be. As a language, the current rules and conventions of European/Western music (e.g., a song in the key of
C major being happier than a song in
D minor) are phenomenally widespread, far more so than, say,
English or
French.
The descendants of the Japanese that Tlogmer describes as finding Mozart dissonant essentially listen to the same music I do here in Australia. The only fundamental differences between J-Pop and Australian pop are things like production style and the language the words are sung in - the harmonies, rhythms and melodies are essentially the same. Moreover, Popbitch has been saying recently that several Mujahiddin in Afghanistan have admitted a love for Bonnie Tyler's Total Eclipse of the Heart, of all things. In 2003, I suspect that the basic rules and conventions of Western music are understood almost wherever you go, largely thanks to American cultural imperialism.
By the way, music is a language (or, more accurately, languages) in many ways, as defined by linguistics: there is a limited amount of language units (ie, notes/phonemes) in both music and speech; the meaning of language units is completely arbitrary in both music and speech; meaning in speech and music is largely conveyed by the relationships between individual language units - i.e., "easy" can mean completely different things based on context, and C major means a different thing if it follows a D major to if it follows a D minor; with both music and speech, we usually intend to convey meaning. The main difference between music and speech is that language has tenses, while music does not; e.g., we have no idea whether a Nirvana song is describing current or past misery.*
Anyway, to extend the idea and metaphor of music as a language, it's perfectly possible to say different things in the same language. To use Tlogmer's examples, the Beach Boys and Nirvana might both be speaking in Rockish, but it doesn't mean, in musical terms, that both of them have to say "i'm picking up good vibrations" or "pain!".
However, Electronicaish and Jazzish might be different but related languages; someone who listens mostly to the likes of Daft Punk can should be able to get the general idea of what Ella Fitzgerald is trying to say. However, this is only a general idea, in the same way that someone who speaks Spanish has a general idea of what someone who speaks Italian is going on about.
*quiet, you.