I think some of the issues you mentioned can be resolved if you have any information regarding the 2 questions Khaled asked in his post.
Specifically,
1. Are there Japanese servers that require whole line sjis/jis conversion? If so, do they support a numeric 005 CHARSET=JIS or some similar value that would tell mIRC to perform whole line conversion?
2. Should mIRC be SJIS/JIS converting non-message lines as well? ie. channel or query names in JOIN, MODE, etc. events?
I think you answered #2 indirectly with your #Japanese thing, but can you clarify on these points?
