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Parma Eldalamberon (Broken Quenya for 'The Book of Elven-tongues') was founded in 1971 as a fanzine devoted to a variety of invented literary languages, published under the auspices of the Mythopoeic Society.
Kēlen is mentioned prominently by Sarah L Higley in her book Hildegard of Bingen's Unknown Language: An edition, translation and discussion (Palgrave Macmillan 2007, The New Middle Ages ISBN 1-4039-7673-2, ISBN 978-1-4039-7673-4) where she discusses Lingua Ignota in the context of constructed languages up to the present day.
A Secret Vice, a lecture given by J. R. R. Tolkien regarding constructed languages