Google Fonts catalog now includes Japanese web fonts, since September, 2018. Google says since shipping Korean in February, it has been working to optimize the font slicing system and extend it to support Japanese. The optimization efforts proved fruitful, as Korean users now transfer on average over 30% fewer bytes than the previous solution.
According to Google, Japanese presents the same core challenges as Korean: very large character set; visually complex letterforms; a complex writing system: Japanese uses several distinct scripts; more character interactions: line layout features (e.g. kerning, positioning, substitution) break when they involve characters that are split across different slices.
To begin supporting Japanese, Google gathered character frequency data from millions of Japanese webpages and analyzed them to inform how to slice the fonts. Users download only the slices they need for a page, typically avoiding the majority of the font. Over time, as they visit more pages and cache more slices, their experience becomes ever faster.
Google has at the moment 900 font families available in the Japanese language: