Okay, here is a first draft (is there an Etoys repository to commit to?). Not bad for an evening's work if I may say so myself ;-)
TTFileDescription does the same thing that TTFontDescription does but operates directly on the files. Download Dejavu and then (for example) execute:
TTFileDescription installTextStyleFrom: 'DejaVuSans.ttf'.
or if you like Arial better:
TTFileDescription installTextStyleFrom: 'C:\Windows\Fonts\arial.ttf'.
Then choose the font from the font menu (Alt-k). I have been able to use Latin, Cyrillic and Greek text together just fine, see screenshot. Unfortunately, I haven't been able to make CJK scripts work; I'm not sure if these aren't included in the normal fonts I'm using or if something's broke. Yoshiki, can you check this?
To my big surprise TTFileDescription is even relatively fast - it renders a glyph in roughly a millisecond which makes it a perfectly reasonable choice to use instead of TTFontDescription. Remaining issues are the lack of housekeeping (if you move the image or the font, you are hosed), the issue that DisplayScanner still tries to render white spaces (tab, cr, etc all show up as boxes) and more testing.
If you have some "interesting" TTFs, please try them out. I'm interesting in finding fonts that don't work and debug them.
Cheers, - Andreas