1. slang, cant, jargon, lingo, argot, patois, vernacular -- (a characteristic language of a particular group (as among thieves); "they don't speak our lingo")
2. patois -- (a regional dialect of a language (especially French); usually considered substandard)
1.
The young men from the Cougourde d'Aix were chatting merrily among themselves, as though eager to speak patois for the last time. - from Les Miserables by Victor Hugo