Short answers, pulled from the story.
In 40 AD, the Roman exile Seneca the Younger reported that natives of Corsica spoke a language he could not understand. This observation marked one of the earliest recorded moments when outsiders noted the island's unique linguistic identity.
In 1859, French replaced Italian as the official language of the island. By 1945, nearly every islander possessed at least a working knowledge of French after decades of policy changes.
The Girolata-Porto Vecchio line divides Northern and Southern Corsican varieties across the island. Northern dialects spoken around Bastia and Corte belong to Western Tuscan groups while southern dialects centered on Sartène and Porto-Vecchio preserve archaic features such as distinction between Latin short vowels ī and u.
An April 2013 survey conducted by the Territorial Collectivity found between 86,800 and 130,200 speakers among 309,693 total inhabitants. Twenty-eight percent spoke well while another fourteen percent understood quite well.
First surviving document containing some Corsican dates to 1220 as a bill of sale from Patrimonio. Legal documents ending late twelfth century show transition from Latin to partial Corsican usage.