By your definition it doesn't require that; it only needs handling for ĉ, ĵ, ĥ, ŭ, ĝ, ŝ and uppercase versions. I think those particular combinations don't exis

By your definition it doesn't require that; it only needs handling for ĉ, ĵ, ĥ, ŭ, ĝ, ŝ and uppercase versions. I think those particular combinations don't exist in any single European language, but you can get Esperanto keymaps ( https://esperanto.stackexchange.com/a/382 https://esperanto.stackexchange.com/a/382 ) But then, Dyalog APL has an IME for entering APL characters and you can do that with standard keyboard keys + modifier (e.g. alt+w for omega in the NARS2000 APL interpreter, ctrl+w in the Dyalog interpreter) - and that's "all" the Windows IME does, support for ctrl+w, but it allows you to do that in any program instead of just in the APL interpreter.