Re:Ask HN: Why can't I call myself “a Japanese”?
by schoen on Thursday October 07, 2021 @08:21PM
(#28793973)
For "English" and "French" we would usually add "-man" or "-woman" ("an Englishman", "a Frenchman"), although people have worried for some decades that the required qualification by sex is too specific.
Maltese, Lebanese, Chinese, Japanese, Polish, English, French - AFAICT only used as adjectives.
Canadian, American, Mexican, German, Russian, Nigerian - adjective or noun.
I'm not even trying to touch on appropriateness, just the general rules on how words are used/spelled. Something about 'an' makes it sound natural to use as a noun.