Isn't English the common academic language?

In a question about university ranking, many people mentioned that language is a privilege for better ranking of English speaking countries.

Isn't a decent fluency in English the requirement for senior academic positions (regardless of native languages)?

Most ranking factors are about research activities. If a professor in non-English speaking country is not fluent in English, how does he supervise graduate students? For supervising/conducting cutting-edge research, someone should be able to read technical literature. Research papers are published in English (and there is no translation normally).

Most non-English speaking countries with excellent higher education (such as Scandinavia, Netherlands, Switzerland) offer the graduate programs in English.

I understand it is easier for native English speakers to read and write in scientific literature, but we don't speak their language, we speak an international language, which is their native language too.

I understand that this requirement is neglected in many countries, but is it reasonable and justifiable to give a senior academic position to someone who cannot read 99% of recent research findings in his field?

Is it acceptable for a professor or even a PhD student to have no understanding of English language? To avoid confusion, consider STEM fields.