"Japanese" is definitely a noun, so it's not grammatically incorrect to say "I am a japanese", but it does sound weird. This is probably related to idiomaticness. In the US, usage of words like "an american", "a canadian" and "a mexican" as nouns generally "sound" ok, as far as popular speech goes, whereas "a british", "a french" and "a spanish", for example, sound strange despite being grammatically correct ("A german" and "a korean" sound a bit weird too, FWIW). As far as I can tell, countrymanship nouns are mostly used with definite articles (e.g. "The japanese participated in WWII"). In other contexts, the rules are mostly based on idiom popularity, if not completely arbitrary. "New yorker" sounds perfectly fine as a noun, but "a san franciscan" is something not many people would ever utter, even in adjective form.

Similar discrepancies can be seen in other noun groups, for example "a beer" is fine, "the wine" is fine, but "a wine" sounds weird.

For the cases where usage of the word as a noun isn't considered idiomatic, people usually say "a korean person" or "a german guy" or "british woman", etc.

"A Japanese" or "a Chinese" were common in English a few decades ago. This has declined very significantly. Interestingly, people often use these as self-descriptions (I think especially non-native speakers).

There is a similar phenomenon with "a Jew", which was once common and where now most speakers would use "a Jewish person" (except, to some extent, for Jews using it as a self-description, although "I am Jewish" is more common than "I am a Jew", but their denotation is also different because the former foregrounds religious identification and the latter foregrounds ancestry or ethnic identification).

Apart from the "person-centered language" phenomenon that other people have mentioned, I think there's the closely related euphemism treadmill

https://en.wikipedia.org/wiki/Euphemism#Euphemism_treadmill

where even a completely neutral term may acquire a negative connotation because of its widespread use in a negative sense, or by people intending to give it a negative connotation. Or people may simply fear that a neutral term has acquired a negative connotation by recalling that it was widely used in the past.

As other commenters have pointed out, there are still demonyms which are common to use in the singular and their idiomaticity has tended to change (mostly in the direction of stopping).

Although I think there's an interesting phenomenon where new countries' demonyms feel plausible to me in the singular ("an East Timorese", "a South Sudanese", "a North Macedonian", "a Kosovan"/"a Kosovar"). It's hard to prove but I suspect that the relative novelty or unfamiliarity of these terms acts to alleviate speakers' internalized fear that they might inadvertently be using the same terminology that was previously used by xenophobes!

But I'm not totally confident in that.

It would be interesting to gather more data by surveying a lot of native speakers about a lot of demonyms and trying to quantify the possible influences of (1) familiarity, (2) phonology, (3) history of ethnic conflict, ...

Another one that feels kind of parallel is the arbitrariness in whether you use a definite article in the name of a country. For example, "the Sudan" and "the Ukraine" used to be very common in English but it's not unusual to see the country names without the article now. On the other hand, "the United Kingdom", "the Netherlands", and "the Maldives" are still always "the". This is different in other languages, where for example "Switzerland" is never "the" in English, but is always "the" in German ("die Schweiz"); "Japan" is never "the" in English, but is always "the" in Portuguese ("o Japão"), as is Brazil ("o Brasil"). It's challenging, though maybe not impossible, to give a clear account of the origins of all of these distinctions...

Edit: in Arabic, too, some countries are "the" and some aren't, but it also doesn't correspond with English practice.

In Portuguese, articles have the additional function of conveying the gender of the noun.

Interestingly, the presence of articles is not actually mandatory, but adding them gives a more colloquial tone, whereas removing them provides a more formal tone, e.g. "China proibe bitcoin" reads like a news headline, whereas a person on the street might say "A China proibe o bitcoin".

I suspect this could be related to learning of word gendering, since communication with children is always colloquial, and article omission tends to only occur when there's an assumption of a minimum level of sophistication.

This observation more or less holds across the entire Portuguese vocabulary, so I think it's quite a different case from the historical analysis of the discrepancy between "american" vs "french" in english.

The degree of irregularity is still striking to me, since you can't have "o Portugal" (even though Portugal is grammatically masculine -- "Portugal é lindo", not "Portugal é linda") but you must have "o Brasil", maybe except for headlines but ordinarily even in headlines. Presumably all native Portuguese speakers are more or less equally familiar with the grammatical gender of both Brazil and Portugal.

Meanwhile, the CPLP members are

"a República de Angola, a República Federativa do Brasil, a República de Cabo Verde, a República da Guiné-Bissau, a República da Guiné Equatorial, a República de Moçambique, a República Portuguesa [which is kind of cheating!!], a República Democrática de São Tomé e Príncipe e a República Democrática de Timor-Leste"

Hmm I think this might be yet another case of colloquialisms. You could most definitely say "O Portugal é lindo" or - in full colloquial fashion - "Vamos pro Portugal".

Even for Timor-Leste, one would still use the masculine article when speaking colloquially, e.g. "Onde é o Timor-Leste?"

As for what word is masculine or feminine, yeah, it's pretty arbitrary.

The China headline example actually has another wonky case: coin in portuguese (moeda) is feminine, yet "bitcoin" is masculine. Go figure!

I somehow picked up the gendering of that word somewhere despite not having set foot in Brazil for about a decade and consuming english media pretty much exclusively for the past two decades. My guess is maybe my brother mentioned it in passing. It's weird how sensitive to learning gendering of new words we portuguese speakers are.

One thing, as the other commenter alluded to: Japanese in US English is almost strictly an adjective, for some reason. Really, any other ese too, including Chinese.

It doesn't sound abnormal to call someone a Korean, or most of the 'an's. But it does to call someone a Chinese/Japanese, as it's only used in the adjective form. We used to have noun forms, but they were deemed offensive long ago - so I'm not sure what the correct way is today.

In general, identity nouns seem to be trending out of use in favor of adjectives (modifying “person” in the most generic, simple case), so the cases where existing ones fell out of favor more completely because of other problems are probably not likely to see general replacement, and even the ones that persist see less use over time with adjectives modifying some other noun being more frequent.

When referring to someone other than the writer/speaker, some see them as problematic because they can be othering/dehumanizing, or they can suggest a (potentially incorrect and offensive to the subject) priority of the particular axis of identity.

Does that mean that I need to introduce myself by saying "I am a Japanese person"? Should I request my colleagues to say "I am an American person" when introducing themselves?

Usually native speakers would prefer the adjective rather the noun in these cases ("I am Japanese", "I am American"), or the prepositional phrases ("I am from Japan", "I am from the U.S.").

Where we don't have a subject pronoun to which the adjective can be attributed, we would usually supply "person" or another noun referring to a kind of person ("A Japanese person told me...", "Any Chinese person would readily recognize the meaning of hundreds of kanji based on the influence of hanzi", "My friend married a Japanese woman", "My mother goes to a Chinese acupuncturist").

I think it's because Japanese and Chinese are nationalities that have been long known by the wider, more xenophbic populace. And they are also used as catchall terms for Asians. For example, the first episode of King of the Hill where the Texans meet Kahn, a Laotian, and Dale repeatedly asks if that is Chinese or Japanese, not understand Laos is a country.

I'm not sure... I was giving it some thought and it seems to me to be more the construction of the word itself.

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.

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.

What was the noun for Japanese?

Japs/Nips, based on Japan/Nippon. These may have always been offensive words, I honestly don't know as it was way before my time, but they both certainly are considered derogatory in the US today.

Which itself is weird, because most other countries we just suffixed - like Englishman, Chinaman(also now considered derogatory, I think), Frenchman, Irishman, etc. But I cannot recall ever hearing 'Japanman' or anything similar.

In any event - I wouldn't take this situation you're in as any slight or bias against any people - it's strictly to do with the English language and ese/ish demonyms.

I thought that these were always considered slang, and that during World War II they became slurs (partly because of their regular use in war propaganda). I don't imagine that there's a time when either term would have been considered a "proper" way to refer to Japanese people, although I do imagine that before World War II they probably wouldn't have been considered insults and might have been considered affectionate.

If my guess about that is right, then you could compare it (pre-WW2 only!) to "Aussie" and "Kiwi" (for Australians and New Zealanders), which nobody would say is "the" name for these groups, but which is also not an insult. Although this is complicated because these are, I think, also autonyms for these fellow English-speakers. Maybe another example is "frogs" for the French, which is mildly disparaging but usually not a horrible insult, at least in contexts that are otherwise respects.

Thank you! There was a very famous Japanese fashion designer named Kenzo Takada. His brand in the 70s was called Jungle Jap. Now the name makes sense!

I wonder if that's intended as a reference to the post-war holdouts

https://en.wikipedia.org/wiki/Japanese_holdout

"Jungle Jap" would be extremely offensive if used by a non-Japanese person to describe a Japanese person today. Although I wasn't born yet, I think that was almost certainly already true in the 1970s.

There are a lot of cases in which people use disparaging group terms and slurs for themselves either as a joke or as a political statement (which is sometimes called "reclaiming" when done consciously and politically). For example, "nerd" is often disparaging but many of my fellow nerds would regularly call each other that in school, and the web comic SMBC routinely refers to its readers as "nerds" (and I don't think the term would be considered disparaging at all when used within the context of a technology-oriented site or forum). I don't think this is a very clever idea for commercial branding, since other people who are aware of the disparaging use might find the brand awkward or uncomfortable!

I'm not so sure about the "offensive" angle - it could be the other way, that is, first Japanese as a noun stops being used (for some reason), and then because of that, using Japanese as a noun starts to sound weird, and then offensive.

Americans have had plenty of racist/hostile opinions against Mexicans or Russians, yet "a Mexican" or "a Russian" remains totally fine.

I think you’d find less confusion if you said “I am Japanese”. It’s not clear to me that “a Japanese” is wrong, it’s just not something I’ve heard before in terms of English phrasing. Similarly, I would likely say “I am Korean” rather than “I am a Korean”.

I've never thought about this before, and it is strange.

From the Wiki article on demonyms though, "Often, demonyms are the same as the adjectival form of the place, e.g. Egyptian, Japanese, or Greek."

I guess you'd also not say "I am a Japanese", but probably just "I am Japanese"?

Similar to how native Japanese speakers often drop particles from their speech, it sounds more natural to say "I'm Japanese" rather than "I'm a Japanese". BTW I'm not American, but Australian. "I'm Japanese" sounds fine to me.

This is because of the "-ese" ending.

For country names ending with "-ese", it's usually an insult to call someone "a" something, like: Chinese, Japanese, Lebanese, Portuguese, or Vietnamese.

With these countries, it sounds better to say "I am from X" or "I am X", such as "I am Japanese".

I'm slightly unpersuaded.

"Have you ever met a Sudanese?"

"She married a Senegalese."

?"He's a Guyanese."

To me the risk of an offensive or disparaging connotation appears especially with East Asian and maybe South Asian -ese terms, but probably not with African or South American -ese terms (and not for "an East Timorese", as I pointed out in another post). I think this connotation arose in English in the 20th century especially with East Asian demonyms, and native speakers may differ in our perceptions of how widely the connotation spread.

It has a vaguely racist or offensive feel to my native U.S. English speaker ears. I don’t know why but it does.

I first thought it was because of World War II propaganda, but on further reflection I don't think that's right, because (1) the propaganda more often used the slang "Japs", and (2) I think "a Japanese" and "a Chinese" were both common in American English for decades after the end of the war (and the American war propaganda was never directed against the Chinese).

I think I favor the theory that someone else suggested in the comments here that the Japanese and Chinese were the only East Asians that most Americans were aware of in the past, and were subject to a lot of hostility and prejudice (both before and after the war), and that people at some point felt that the singular noun forms had acquired a possible interpretation as slurs because of the memory of this. That matches my understanding of "a Jew", which of course is the perfectly normal and traditional form in English, but which many non-Jews and plenty of Jews have become uncomfortable with as a singular noun.

In Spanish no one cares if something is a noun or a proper adjective.

There is "chino, japones, italiano, frances, aleman". Full of different Romance suffixes and we put functionality over ideology.

Too lazy to care, and the noun/adj. roots and suffixes go back to the Latin spoken since the Romans.

We have "ingles" and "britanico" too, yet no one would say a common used demonym can be racist.

Also, hey, any demonym can be used either as a noun or an adjective. Both for people and for things.

It sounds racist, even if you say it about yourself. Liberal thinkers are worried about depersonalizing via language so they use phrases like "they are X-ese" or "they are an X person". While the phrase "they are a X" is considered a more derogatory tone that replaces someone's person-ness with their nationality.

It doesn't look racist, but depersonalizing.