So, I was incorrect about what's required for CJK - apparently, as long as the fonts are installed at the OS level they should display within Vision/the Designer, because we'll "fall back" to the OS to display them.
As for Vision's custom keyboard layouts: basically they're just that, custom. So if you want to support additional languages, such as Chinese characters, you can do that by creating a new custom keyboard layout. The exact nature of that layout is basically up to you; we don't put hard restrictions on the number of characters or 'accents' they can have.