Always worth read: How to write unmaintainable code

Masking

Writing the roman numeral IIII instead of IV is not uncommon on clocks: https://www.deutsches-uhrenmuseum.de/en/museum/knowledge/clock-facts/clock-dials-with-4-iiii-or-iv.html

Nothing a Wi-Fi controlled power outlet can’t fix. If the printer is turned off it can’t suddenly start printing.

making room for all conceivable characters within a language, and even accommodating multiple languages

reads like snakeoil… Why not design the algorithm to work on arbitrary blocks of bytes so you don’t need to care about „characters“, just like any real-world encryption algorithm?