I find it sort of implausible that somebody high in their field is totally ignorant in English, if only because so many papers are only published in English.

I've known so many researchers who apologize every other sentence because they say they've only read English and I would never had known otherwise.

Which is to say - it'd be wierd to say "well I don't know English and I don't know anybody who does oh well". But, anyway, the papers were published on aeXive in...

There are plenty of Japanese scientists who are _at least_ extremely uncomfortable in English. Plenty of people who struggle to write their own stuff in English and get it corrected a lot. Though I think that beyond a certain level you have to be interacting internationally to get anywhere in your career so you're gonna be forced along.

Plenty of people would learn Latin to consume some content, but doesn't mean they are proficient in it itself, would be another example.

Having said that, I think that in the research field that merely ends up with "very confusingly written papers with mistakes large enough to hide process errors" more than "cannot communicate any info in English". But there are plenty of people who get their doctorate and their only English-language output is their final papers in themselves.

You realize there’s an incredibly obvious selection bias in your sample?

If you mean I am not aware of the ones that don’t speak English, not really, I have worked and gone to university in Japan and know a large number of people with whom I only speak in Japanese because their English skills are not good. Among working research physicists (not just Phds working on some company) under 45 I have found solid English skills as a rule, probably because international experience is important to their careers.