It means language so altered as to be unintelligible. The word itself is strange and uncouth, perhaps part of the reason why it has only rarely been used in English. It’s sixteenth-century French and comes from two words in the Breton language, bara, bread, and gwin, wine. It is said that Breton pilgrims on their way to holy places demanded bread and wine from their hosts in inns along the route. The innkeepers, not understanding their language, created baragouin as a word for a language so strange as to be unintelligible.
The story became confused in the famous dictionary of the French language compiled by Émile Littré in the nineteenth century. He said it was probably from bara + gwenn, white, in reference to the exclamation of Breton soldiers at seeing white bread for the first time.
A classic use was in Two Years in the French West Indies of 1890, in which Lafcadio Hearn commented on the strange speech of black slaves: “He had scarcely acquired some idea of the language of his first masters, when other rulers and another tongue were thrust upon him, — and this may have occurred three or four times! The result is a totally incoherent agglomeration of speech-forms — a baragouin fantastic and unintelligible beyond the power of anyone to imagine who has not heard it.”
In the nineteenth century, it turns up in the speech of East End Londoners in the forms barrakin or barrikin with the sense of gibberish, double-Dutch, or a jumble of words. A rare sighting is in Henry Mayhew’s famous work, London Labour and the London Poor, of 1851, quoting a costermonger (a street seller of fruit and vegetables) on the difficulty of understanding Shakespeare: “The high words in a tragedy we call jaw-breakers, and say we can’t tumble to that barrikin.”
Some writers have suggested that the verb barrack, to jeer derisively at somebody (or to shout in support of your team if you are Australian), comes from the same source. But the experts prefer to point to the Northern Irish dialect word of the same spelling (which may be linked to the Scots berrick) that means to boast or brag, a word that my references say is still known among schoolchildren in Belfast.