I, at least, literally made my own keyboard layout some years ago, to be able to type all the characters I want. Got versions both for Linux and Windows (haven't had a need to use Mac yet).
It's basically an extension of US International which can type every letter in all the Latin based alphabets and most of the common punctuations, including hyphens, hyphen-minuses, en-dashes, and em-dashed.
Never found room for all the Greek letters, though.