From a comment by composer and poet Samuel Vriezen to my last post:
Years ago, I gradually came to feel more and more that the whole notion of a 'crisis of language' that would have come with atonal practice is extremely misleading and has led composers to confuse languages and compositional methods (and leading to sometimes very arbitrary ideas about how to 'construct' a language - you find this tendency among academic modernism just as much as with people who decide to write in what they think of as an 'accessible' style). Whereas in early free atonal works it's so clear that works, in all the aspects of musical thought, are constantly referring to existing musical language.
I agree with Vriezen, especially about our tendency to hear works of music as determinative of subsequent works, which has the effect of re-writing the earlier music into the narrative that happened to "win", rather than the concerns of the moment. We encounter revisionism of this sort all the time, not only for the tonal/late tonal/atonal/serial cluster but for the embalming of the later works of Mahler into a death narrative (a death the composer hardly anticipated), elevating Shostakovich or Britten to heroes of political or social resistance, or the (in part, commerce-directed) series of repackagings of the minimal/ist/ism label. Renewing our acquaintance with a given music, as listeners, performers, and composers, has got to be about learning to listen to the music with ears as fresh to the possible consequences that the music embodied and implied in its moment of origin as to the limited consequences that actual music history followed. The luxury here presented by music comes by virtue of its ephemeral status; when a work of music is revisted and reconsidered, its implications are still fresh and can result in entirely new modes of listening, styles of performance, and, in response, new composition. Music history is not necessarily a straight narrative, and no cul-de-sacs in musical history are necessarily dead ends. That's why some of the most interesting free atonal or minimal music is being composed now, and that's why we may usefully consider the possibility that Mahler could have been (and indeed, was planning to be) around long enough to write another half-dozen or more symphonies, maybe even an opera or two.
But, if I might be permitted a tangent, I'd like to go a bit further on one point. Perhaps it's time to take some steps away from the use of the work "language" with regard to music. Sure, music and language share features and, from the non-negligible physiological standpoint, share a whole collection of perceptual and cognitive organs. But it's not unusual that organs have multiple functions or applications; that whole assembly of organs known as the mouth is used for breathing and nourishment and the occasional bit of regurgitation as well as the whole swathe of acculturated oral pleasures, among which speaking and singing are but two. We're pretty well obsessed with the relationship between speech and singing, but that between breathing and singing is as important, and the relationship of song to other non-verbal utterances is presumably non-trivial. Speech and music do, indeed, share the hearing apparatus, but the phonology of speech, as demonstrated by sign languages, does not require any acoustic component, it may be entirely visual.
As far as I'm concerned, a much more interesting case of sharing organs does take place in the ear, which are not only good for listening, but also house the organs for equilibrioception, which keep track of angular momentum and linear acceleration, through which the body senses its movement, direction, and acceleration, and thus attains and maintains postural equilibrium and balance. In combination with the echolocative functions of listening, the ears are absolutely critical to our perception of space.
The cluster of questions that I'm touching on here often comes back to the question of the origin of music, and many linguists (and, to be fair, musicians) like to present music as a bonus — Marxists might speak of a superstructure (Überbau) — piggy-backing on top of the organs and structures used by language, which is considered essential for human survival and development. But the possibility of music's orgins in some fairly complex spatial and temporal functions, with the closely related phenomenon of dance, is not to be neglected. Indeed, one may well take to song not to communicate, as heightened speech, this or that (anyone remember Mel Brooks' 2000-year-old man, who stated that the first song was "A lion is eating my foot off, somebody call the cops!") , but rather to help find your way in the wilderness or to keep track of passing time.