There are two languages of Pitcairn Island, English and Pitkern

Pitkern

Pitkern is a creole language based on an 18th century dialect of English and Tahitian. It is a primary language of Pitcairn Island with fewer than 100 speakers worldwide. However, the closely related Norfuk language has a few thousand native speakers...

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Pitkern is a creole language based on eighteenth century English and Tahitian

Tahitian language

Tahitian is an indigenous language spoken mainly in the Society Islands in French Polynesia. It is an Eastern Polynesian language closely related to the other indigenous languages spoken in French Polynesia: Marquesan, Tuamotuan, Mangarevan, and Austral Islands languages...

 and spoken by about fifty people inland not to mention those outside Adamstown, mostly dozens of children leaving Pitcairn while becoming adults. It is partly derived from eighteenth century English because Pitcairn Island was settled by the Bounty mutineers

Mutiny on the Bounty

The mutiny on the Bounty was a mutiny that occurred aboard the British Royal Navy ship HMS Bounty on 28 April 1789, and has been commemorated by several books, films, and popular songs, many of which take considerable liberties with the facts. The mutiny was led by Fletcher Christian against the...

 in the eighteenth century, and they brought some people from Taihiti with them.

Pitkern is closely related to Norfuk spoken on Norfolk Island, where some descendents of the mutineers subsequently settled.