Shirl:
To be eligible for a private pilot certificate, a person must:
[a, b...]
(c) Be able to read, speak, write, and understand the English language.

Cubdriver:
But the pilot in question almost certainly never applied for a (US)
private pilot certificate, or indeed any American pilot certificate.

Yeah, I realized that afterwards.

Is there a requirement that a pilot holding a foreign certificate and
flying in US airspace "read, speak" etc the English language? Or
merely that he communicate with ATC in English?

I don't know. Haven't seen one, so far. Again, just seems any pilot
flying into JFK, SFO or LAX should speak and understand English well
enough to be able to answer a question as basic, whether it's "standard
aviation phraseology" or not, as "Have you been cleared to the ramp?"
and to understand and accurately read back a clearly spoken taxi
clearance without having to hear it four times.

Maybe it's just me, but if a controller asked me the same question a
second time, I'd think about what I didn't answer instead of just
repeating the same response without even thinking about it.