Kdammers is running the current version of Mozilla on Windows 7 with a dual-script keyboard. Typing in Hangul (한굴) is not working in VisualEditor: letters can be removed but when they are typed, they just disappear.
Stefan2 did some related testing:
Ibus-hangul (Korean) seems to work correctly in Firefox 32.0. In Chromium 37.0.2062.94, it produces spaces instead of Hangul letters. However, if a syllable only consists of two letters, the syllable shows up after typing in the second letter. It seems that syllables consisting of more than two letters can't be typed in using Chromium.
Anthy (Japanese) is broken in both browsers.