When talking about a person from Japan, why is it offensive to say "a Japanese" rather than "a Japanese person"?
The English language Wiktionary says
(person in or from Japan): The singular “a Japanese” is less common
than locutions using the adjective, such as “a Japanese person”, and
is considered potentially offensive by many speakers.
but doesn't explain why it is offensive.
Allwords.com says
Note: many people object to the usage of this sense in singular form,
and it is now more frequent to see a person in or from Japan referred
to by using the adjective Japanese. Rather than "a Japanese," you will
frequently see "a Japanese person."''
but again, there's no explanation.
Best Answer
I found an answer in this article: 「私は日本人です」は、I am a Japanese. それとも"I am Japanese?