Dr. Chen's English is very good. He has a vast vocabulary and can comfortably converse about topics as varied as medicine, philosophy, politics and history.
However, one peculiarity that I've noticed is that Dr. Chen often pluralizes words that ordinarily should be singular. My brother and I find this funny and even look out for it.
One example is that Dr. Chen will often say "the peoples" instead of the grammatically correct "people". He'll often say things like "In China, the peoples are tired of the government. They know that the government is so stupid and liars."
With the example above, one could assume that Dr. Chen adds the extra s to "people" because that word is semantically plural and so he is simply adding a regular pluralization marker to an irregular plural, maybe unable to stop himself in rapid speech, but in reality Dr. Chen also frequently adds the same extra s to words that aren't even semantically plural or words that are never pluralized.
The following are some examples of this:
"I'm a big fan of the English footballs."
"I like the Liverpools."
"I've been to the Perus and the Brazils. I saw the Machupichus."
Curiously, Dr. Chen also adds the plural s to Chinese words related to TCM. For example:
"The energy is produced in the qihais."
"All of the yin meridians join together in the baihuis."
The qihai and baihui are both singular concepts in TCM.
Dr. Chen isn't the only Asian who does this. I looked on the internet and found posts on Reddit talking about Asian people who pluralize non-plural words while speaking English.
I don't understand why some Asians do this. Most Asian languages including Mandarin don't even explicitly mark the plural in most cases. It is simply understood through context. Exact quantities are usually expressed by special count words placed before the noun. So one would expect that Asian speakers would be more likely to omit the marked plural forms in English and other European languages rather than adding them superfluously.
In fact, I used to hear Chinese immigrants speaking Spanish in Spain and they often don't pronounce the s plural marker (Spanish pluralizes nouns - and adjectives too - in a similar way to English with -os, -as and -es being the main pluralization suffixes, even though interestingly, from an etymological standpoint, the s plural marker of Spanish, French and Portuguese and that of English aren't even related). I've heard them say things like "lo' maricone'" instead of "los maricones", etc.
Like this Chinaman who lives in Madrid and claims to be fascist dictator Franco's biggest fan (lol!):
By the way, this Francoist Chinaman is also called Chen!
And his wife too!