The Raspberry Pi 400 is essentially a Raspberry Pi 4GB housed inside of a keyboard. The Pi 400 does come with a 1.8GHz clock speed boost, 300 MHz more than the Raspberry Pi 4. Although with a little tweaking this extra speed boost is easy to replicate, and exceed on the Pi 4. If you have a Raspberry Pi 4 with a certain serial number, then the latest Bullseye release will even do the overclock for you.
The Japanese layout is a big deal for what’s essentially a computer inside a keyboard, and the new Japanese keycaps join ten others, from US and UK to Portuguese and Danish,
The JIS keyboard layout keeps the roman letters alongside the hiragana. Special language input keys switch between input methods - note the extra keys alongside the space bar and below Esc on the new Pi 400 keyboard - and to fit Roman characters into the squares used by typical Japanese characters in order to preserve the grid-like look of a block of text.