The font linking feature is enabled by default now as this ensures that all characters are displayed correctly. It can no longer be turned off in newer versions of mIRC.
That said, I tested the display of Japanese characters in both v6.35 and v7.25 under XP, using both FixedSys and Verdana as the set font, and they both appeared the same. I have not had a chance to test under Windows 7 yet.
Font linking is dependent on the fonts installed on your system. The font linking method in mIRC should use the set font as the default and will only try another font if characters are not supported by it.
In the case of Verdana, which does not support Japanese characters, it looks like Windows is performing the font linking itself (using a particular font) when "font linking" is disabled in mIRC. When "font linking" is enabled in mIRC, mIRC searches the following fonts in this order to find character support: Microsoft Sans Serif, Arial Unicode MS, Tahoma, Arial, Lucida Sans Unicode, Code2000, Fixedsys Excelsior 3.01.
I plan to change the way mIRC displays text in future to use Windows to perform the font-linking instead of its own routines (although that may have side-effects, such as not displaying older fonts properly) which may resolve issues like this.
