That's interesting. I'm a bit spoiled by primarily using Vim to write code and prosé in American English. Vim's digraph feature (Ctrl-K by default) has handled unicode char input nicely enough for me, but I wonder if the compose key could be of use when writing text in Japanese for example.

I actually meant to do it systemwide, for when you're writing or googling things not in English, or when you want to write a fancy ⅝. The day I have to start putting diacritics into computer code is the day I quit programming:)

I think it's no good for Japanese, but I know very little about Japanese input. Romanji is still Japanese, right?

Now that's an idea. Haskellers routinely use x' as a variable name, but ẋ and x̃ are also valid ones!

I use option-e e to insert é, option-n n to insert ñ, etc. I noticed this while pressing option in the Keyboard Viewer.