Charles Duff (1894-1966) was born in Enniskillen in Northern Ireland. After the Great War (and after the Second World War) his output was mostly linguistic (All Purposes French for Adults, Italian for Beginners, First Year Russian, German for Beginners, How to Learn a Language, The Basis and Essentials of Portuguese, and so on). He did, however, write a science fiction play, Mind Products Limited: A Melodrama of the Future in Three Acts and an Epilogue (1932). It depicts the world of 1960, and imagines a world involving mind control (and X-ray vision), carplanes and television phones, “a Čapek-like vision of totalitarianism in a world gone—subversively—mad” as John Clute puts it in the Encyclopedia of Science Fiction. He also wrote Anthropological Report on a London Suburb (1935), as by Professor Vladimir Chernichewski, which has science-fictional tones: it is a satire which views British society as through the eyes of an anthropologist. According to Wikipedia, he also published a short story in 1936 called “The Haunted Bungalow”.
I have no information yet about his life, except what is in a brief article in Wikipedia. He apparently joined the Foreign Office towards the end of the War, and resigned from it in the 1930s, “claiming it was solidly supportive of fascism in Spain and ready to back a similar system in Britain”. After he retired, he taught linguistics and languages in London and Singapore.