As a non-native English speaker who speaks 4 languages, I have almost never found myself using any other language than English in a code editor or IDE. And I never seen anyone who did, except for very occasional editing of localisation data files.
I have seen used (mainly in comments): Japanese, French, German, Dutch, Chinese (don't know if it was TC or SC; if those are even different unicode ranges or whether they are differentiated by font), and, if I remember correctly, Afrikaans. It's also kinda funny and a little off-putting to see English keywords side-by-side with, like, Dutch variable names.
