The much-loved “jive talk” scene from the comedy film Airplane! is an amusing if slightly improbable demonstration of how a single language – in this case English – can accommodate varieties so divergent as to be mutually incomprehensible.*
A more plausible form of the phenomenon appears in John McWhorter’s book The Power of Babel: A Natural History of Language, in which the author recounts an incident that neatly depicts the existence of such varieties in a language, one perfectly transparent to him and the others increasingly unintelligible.
The dialects in question are Standard English and Guyanese creoles. McWhorter was at a conference when he entered an elevator with his dissertation advisor; another Guyanese man hopped in at the last minute:
They started out speaking Standard English, largely in deference to me, but as the elevator went up and their conversation became gradually warmer and more spontaneous, they started gliding into increasingly more creole layers of their speech repertoire. The higher we went, the less of their conversation I could grasp. I lost the first sentence above the fifth floor; by the tenth, all I knew was who they were talking about; by the eighteenth, all I knew was that something was really funny and that it probably wasn’t me. By the twenty-fifth floor, when we got out, they might as well have been speaking Turkish. Yet to them, they had never stopped speaking “English” – they had simply traveled along a continuum of creolized varieties of it leading away from the lone vanilla variety I grew up in.
What I like about this anecdote is the incremental but radical spontaneous morphing of the language, along with the readymade metaphor (an elevator) in which the continuous shift takes place.
Ethnologue’s page on Guyanese Creole English also notes the “continuum of variation from basilectal Creole to acrolectal English of the educated”.
* Sometimes this communicative shortfall hinges on a single word, as in the famous case of William Caxton’s egges/eyren.