Irish Travellers speak English and sometimes one of two dialects of Shelta — Gammon (or Gamin) and Irish Traveller Cant. Shelta has been dated back to the 18th century but may be older.[37] Cant, which derives from Irish, is a combination of English and Shelta.[38]
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Shelta is a cryptolect (secret language). Irish Travellers do not like to share the language with outsiders, named "Buffers", or non-Travellers. When speaking Shelta in front of Buffers, Travellers will disguise the structure so as to make it seem like they are not speaking Shelta at all.[42] There is fear that if outsiders know the entirety of the language, it will be used to bring further discrimination to the Traveller community.[43]
This sounds suspiciously similar to "Theives' Cant" from 1E and 2E AD&D.