In order to use Eastern encodings, however, you have to turn Unicode support off and run mIRC in a locale appropriate to that country, either by changing your system settings or using Microsoft's AppLocale utility.
Er, no you don't - you just select an appropriate font (MS Gothic for Japanese, MingLiu for Chinese BIG5, SimSun for Chinese GB2312, etc.), select the appropriate character set (as mentioned previously), then set UTF-8 to "Display only". The only time you ever
need to change the system locale (either globally or using AppLocale) is if you are running Windows 9x/ME - for NT/2000/XP, you just need to install support for the language once (to get the fonts and the codepage conversion tables) and you're good to go.