Cyphers are letter-exchangers, trading one letter for another to make a code that may or may not be pronunciable; some cyphers use numbers and symbols as well. I’ve been using cyphers since 2002 or so; Kommu, the oldest of these, is so familiar to me that I can translate on the fly (albeit slowly). I usually use cyphers for non-English languages in fiction, but Kommu has also been used in class and in the workplace since its invention.