Dunno about China, but Japan is a weird mix of two systems: - Groups of 4 digits separated by the corresponding power-of-10000 kanji, e.g. 1億2345万6789. Makes s

Dunno about China, but Japan is a weird mix of two systems: - Groups of 4 digits separated by the corresponding power-of-10000 kanji, e.g. 1億2345万6789. Makes sense, I would say it's actually better than just separating the digits, as it makes easier to recognize the size of the number. - Groups of 3 digits separated by commas, e.g. 123,456,789. I asked around how they do to mentally regroup digits by four, and everybody told me that is quite difficult and don't understand why they don't group digits by four. Then again, they have the most difficult writing system in the world and a ridiculous calendar, maybe they just like challenges.