I don't presume to know what they meant, but as an example of something I think fits the bill, I downloaded "Bill Bailey Won't You Please Come Home" and the lyrics are full of a certain type of phonetic transliteration from vernacular Afro-American English (as if it's a foreign language or something) the likes of which you would probably never see today (e.g. lots of "dat" and "dey" and "throw'd" and "de whole day" and so on).