Do we call a person from China "a Chinese"?
For example, can I say: I have a friend, he is a Chinese?
Do we call a person from China "a Chinese"?
For example, can I say: I have a friend, he is a Chinese?
He is a Chinese is okay, just like She is a Portuguese is okay. But probably most native English speakers prefer to say He's Chinese and She's Portuguese.
See the Wikitionary usage note about a Chinese:
As with all nouns formed from -ese, the countable singular form ("I am a Chinese") is uncommon and often taken as incorrect, although it is rather frequent in East Asia as a translation for the demonyms written 中国人 in Chinese characters or Japanese kanji.
The word Chinese is both an adjective and a noun.
Someone who is from China is a Chinese (noun) or is Chinese (adjective).
However, it's more common to use Chinese as an adjective i.e. he is Chinese.
To describe your friend from China, you would say
He is Chinese.
He is a Chinese (person)
although the first gets used more often.
More formally, the Immigration authorities might say
He is a Chinese national.
he has a Chinese passport
if he was the only Chinese in your school, you might say
He is the Chinese at our school.