... Psalmanazar decided to make his identity more exotic, and posed as a Japanese convert to Christianity. To facilitate the project, he revised the certificate that he had had drawn up to prove that he was Irish, and devised an alphabet and many words of a language that he thought might be taken for Japanese. Aware that Hebrew was written from right to left, he imagined that other ‘oriental’ languages would follow that pattern. He invented twenty letters with shapes, names, and pronunciations that resemble some Greek and Hebrew letters. By his own account, he also added ‘many other particulars equally difficult, such as a considerable piece of a new language and grammar, a new division of the year into twenty months, a new religion, &c. and all out of my own head’ (Memoirs, 137).
... this time [he] used the name of Salmanazar (ibid., 169), which he took from the name of a biblical king of Assyria and captor of the Israelites, Shalmaneser (2 Kings 17). Later he began spelling the name with an initial P to make it more exotic.
... [H]is fanciful account of Formosa, which occupies little more than half of the book's 327 pages ... raised doubts about his veracity in several quarters at the same time as it excited many readers. Among his entertaining but suspicious claims were that Formosa was Japanese rather than Chinese; that the state religion, founded by an avatar named Psalmanaazaar, required the annual sacrifice of 18,000 boys under the age of nine; and that the production of children was facilitated by the encouragement of polygamy, although adultery was absolutely forbidden.
... [Regarding other cases of false identity and forgery in the 18th century]: In these and many other cases of forgery and assumed identity in the period, the impostor imagined he had access to hidden information and that he himself was in touch with a deeper or older, often more ‘natural’, tradition of knowledge than that accepted by the current establishment. The flourishing of such forgers at this time may have been a response to the increased professionalization of knowledge during the period. Psalmanazar's quarrel with the Royal Society, his defence of revelation in religion, and his immersion in ancient Hebrew may be all regarded as a rebellion against modern forms of knowledge.
OK, so a "defence of revelation in religion, and an immersion in ancient Hebrew" are rebellions against modernity, are they? Well, count me in. Vive la revolution!
Happily, Psalmanazar eventually recanted his lies, became a believing Christian and a friend of the young Samuel Johnson. He died shortly before Johnson first encountered James Boswell in a London bookshop.