The only difference I see is the Chinese market is large enough that you don't need to appeal globally.

That's true for Japan too, though. With 125M people, there are plenty of local incumbent apps and tech companies that don't feel any need to compete globally.

I think the population factor plays here.

China has more developers that speak English than Japan does and they’re ~all in Shanghai, Beijing or Shenzhen because that’s where the money is. Shanghai is substantially easier to get around with very bad Chinese than Tokyo is with very bad Japanese.

Overwhelmingly majority of dev in Shanghai (or China in general) are still native Chinese. "Easier to get around with very bad Chinese" isn't a factor, at all. Not even rounding error.

China is better than Japan in software development simply because they pay (much) better, which causes more people (esp. more "smart" people) to pursue this career for the money.

And the reason why Japan doesn't pay software dev as well is in the article.

I think it’s more than just language but in this case I think the relative economic history is a factor: Japan had a large modern economy so there were tons of jobs working at domestic companies building with domestic tools. Modern China’s economy & educational system developed later and a lot of high tech work was dominated by American companies. I think that meant there was a generation where an equally bright engineer in Japan could think they’d have a solid job at one of the biggest companies in the world and never need to be highly proficient in English but their Chinese counterpart would make the opposite decision.

We’re at a really interesting point where that calculation may be reversing with China being a huge domestic market with strong pressure for independence.