I had edited my previous post while you replied. This shouldn't be an issue with gtsdll, as this has happened with simply having correctly displayed Japanese characters in the channel window (with the Western script). I can't recall there ever being a crash in the chat window where I had Japanese as font script since the time I had changed it to Japanese there (should've noticed this when I did the change, but I still thought it was about the font).
*Edit: before someone says this is because of gtsdll sending mirc crap it can't handle, that's not entirely true. I can't make it crash by simply copying those same characters straight into the chat window, it displays the characters correctly and nothing happens. However, when I use the gtsdll command /aud in a different chat channel, it displays the characters correctly and does not crash. The difference is in font script. In the channel it didn't crash I use Arial Unicode MS with Japanese script, in the channel it displayed garbage and crashed I use Arial Unicode MS with Western script. Why Western script can display Japanese characters often times just fine, but occasionally crashes on them, I have no idea.