I figured out what was wrong: LSM:Register() now requires 4th argument for fonts to work on non-western locales.
lib.LOCALE_BIT_koKR = 1
lib.LOCALE_BIT_ruRU = 2
lib.LOCALE_BIT_zhCN = 4
lib.LOCALE_BIT_zhTW = 8
lib.LOCALE_BIT_western = 128
If your font contains korean, cyrillic and latin symbols (or more like if you want the font to be available on RU/KR/EN/DE/FR/etc. locales), your 4th argument must be 131 (128 + 2 + 1).
An example:
LSM:Register("font", "qfont", [[Interface\AddOns\nibRealUI\Fonts\qfont.ttf]],
2)