Rb doesn't load font entirely. (Absolutely no problem with latin characters)
What I saw is when some glyph is needed to be displayed, rb loads that glyph on the fly (for first time) and save 'which character it was' to font cache (.glyphcache), so rb can load those glyphs on next boot.
I use fat multilingual font and increased MAX_FONT_SIZE to 600K because on default 60K, it fills instantly on first file browsing, so when it needs to display uncached(not cached because font buffer already hit MAX_FONT_SIZE) glyphs, extra loading from the disk happen every next time.
1st problem, If font size(fnt file) is smaller than MAX_FONT_SIZE, all glyphs are messed up.
2nd, loading large font(I tested 400KB, 2800KB) on booting causes heavy seeking, and needs 60+secs. (I think it is because rb doesn't load font continuously (1st glyph, 2nd, 3rd, 4th, 5th...) but load cached glyph discretely like 2nd, 4th, 15th....
So I think an option to completely load fonts would be nice,
and font smaller than MAX_FONT_SIZE should be handled correctly.