There's this Quartz article on how Chinese fonts are made with this curious claim:
This has been possible for a number of years, but Chinese always posed a particular problem: with so many glyphs, the fonts require huge downloads for users that have not visited the site before, putting a strain on bandwidth both for user and provider. (A Chinese font can run up to 6 or 7 megabytes for a single style and weight. Compare that to PT Serif—Quartz’s body font, which covers over 100 Latin languages—which is just 1.4 megabytes for four styles.) Now Chinese webfont providers cleverly scan through a webpage’s text to identify which glyphs are required, and send only those to the user instead of all 13,000-plus.
Is it possible for a website to serve only part of a font to render text? How do browsers download these incomplete fonts? And does it relate to font subsetting with unicode-range?