The delta speaks the central Tamil register that standard written Tamil is closest to, which means the interesting variation here is not geographical so much as social and historical. Three separate court and migration events left languages behind — a Telugu-speaking Nayak administration in the sixteenth century, a Marathi-speaking Bhonsle court from 1676, and a French administration in one enclave until the 1950s — and all three are still audible.
Central (delta) TamilDravidian, Tamil
The register that schooling and broadcasting treat as unmarked. Its own markers are audible mainly to speakers from elsewhere — a fuller vowel in the second syllable and a slower delivery than Madurai or Coimbatore speech.
Brahmin Tamil of the delta agraharamsDravidian, Tamil
A well-documented social dialect with distinct kinship terms, a heavy Sanskrit lexicon for ritual and food, and Marathi and Telugu borrowings picked up from the courts the community served. It is the variety film and television use as shorthand for Kumbakonam.
Thanjavur MarathiIndo-Aryan, Marathi
Marathi as spoken by descendants of the Bhonsle court and its retinue, isolated from Maharashtra since the seventeenth century and consequently retaining older forms while borrowing Tamil syntax. Written in Devanagari, Modi and occasionally Tamil script.
बोलने वाले: A few tens of thousands, mostly older
SaurashtraIndo-Aryan
Spoken by silk-weaving families settled in Kumbakonam and Thanjavur as well as further south, and carried here by the same migration that shaped Madurai's textile trade.
Karaikal French residueRomance, in loanwords only
Not a spoken variety but a vocabulary — administrative, legal and municipal terms surviving in Karaikal usage and in property records from a period when the enclave was governed from Paris.