This Bakhtin listserv summarizes heteroglossia and suggests some authors I ought to read.
For instance, Karine Zbinden: “Bakhtin begins his argument about centripetal
and centrifugal forces with a few historical observations…[and]…details the diverse ways in which other ‘dialects’ have been suppressed….Heteroglossia thus accounts for both the common social nature of language as a shared code and for the individual appropriation of language in use.”
Another link with great quotes, to wit:
p.272 But this occurs in the midst of heteroglossia, which grows as long as language is alive.