Chinese papers are (with much higher probability) citing Chinese sources. It's a self-empowering cycle, which doesn't say anything about the quality.

Yes, and American papers are much more likely to cite American papers. Science is more international than the vast majority of professions, but there are absolutely still state cultures that are just more likely to have read research in their language, published by someone who's a friend or a friend of a friend, or have national institutions which concentrate scientific talent that make scientists be colleagues. Nowhere near as strong of an effect as other jobs, but it's still there.

Ethnocentrism is ethnocentric.

It's like how historical American medical data collected by universities has been misapplied to pharmaceutical and medical practice because of demographic bias. Research participants largely matched the demographics of the university: healthy white males.

Or more broadly, whenever you see a "last name" requirement on a form, you know it's software made by people who think it's normal for people to have "last names", and that everyone should know what that means.

This just in:

Researchers are vastly more likely to read, and therefore cite, papers in languages that they understand fluently.

Virtually all of this work is published in English though, even from the Chinese researchers.