There's no translations for official websites far as I know, so it should be the official website, the JP one.

(Unless that has been changed, but for series it's still like this at least)

As far as I know localized websites are possible for movies, just not for series. I confirmed it by trying to delete the website for ja-JP and then the en-US one stayed.

Edit: And it says so in the bible too: https://www.themoviedb.org/bible/movie/59f3b16d9251414f20000001#59f73b759251416e71000008

I know that movies can have different official sites for each language; otherwise, I would not have submitted this report.

Since I posted the original report, the English title of the movie has been changed and locked.

The grammatically correct Unicode character for a horizontal line marking divisions between parts of a title is the en dash (–).

The hyphen-minus (-) is commonly used online due to the historical inconvenience (though not impossibility) of entering dash characters in Windows and the predominance of that operating system, and the popularity of IMDb, which uses an ancient text encoding system which cannot handle dash characters.

Hyphens are for joining words together to form compound words, and only that. The only time a hyphen should have a space on any side is when one is listing several words which share a part and only mentioning the shared part once, like "lemon-, orange- and lime-flavoured sweets" (to go for the first thing that comes into my head; yes, I know one could describe all those as "citrus-flavoured", but then it wouldn't serve as an example).

Being commonly used does not make it correct.

So I believe the correct way of formatting the official English title is Demon Slayer –Kimetsu no Yaiba– The Movie: Mugen Train.

While the version with hyphens, Demon Slayer -Kimetsu no Yaiba- The Movie: Mugen Train, which is commonly found online, should be an alternative title, with the type "alternative formatting".

Being commonly used does not make it correct.

Ya, I don't know if I've ever seen en dash being used by the distributors outside of a few Apple TV+ originals. You're basically asking for a site-wide policy change. I don't believe this is a decision that I should make.

So I believe the correct way of formatting the official English title is Demon Slayer –Kimetsu no Yaiba– The Movie: Mugen Train.

Can anyone confirm the English on-screen title?

That is the title from the official subtitles on the Japanese Blu-ray: https://i.imgur.com/3INz0kD.jpeg

Thank you for posting that image, as as well as it being useful here it's one that I can link to to try to prove to IMDb and elsewhere that the English title isn't Demon Slayer: Kimetsu no Yaiba the Movie: Mugen Train, as many English-language sites seem to have decided on.

Regardless of which is decided on, TMDb needs to have a rule on whether dashes in at least Roman-character titles (to begin with) should be represented by actual en dash characters (–) or by hyphens (-). IMDb uses hyphens, though that's grammatically incorrect (hyphens should never be spaced on both sides, etc.) because of the old text encoding system it's stuck with; Wikipedia and other Wikimedia projects use en dashes because they use Unicode, so can use the correct character. As TMDb uses Unicode, I would think unless told otherwise that it would also use en dashes.

I know that it uses straight apostrophes and quotation marks, but Wikimedia uses Unicode en and em dashes but straight apostrophes and quotation marks, so it doesn't inherently follow that if you don't use one kind of non-ASCII character you also don't use any others, and there's at least one title on TMDb not submitted by me that has an en dash in it. There are others, like Star Wars entries, that currently have spaced hyphens in them, but that could be because they've been copied from IMDb, or entered by someone not aware of the existence of a character for en dashes.

It's not sufficient to say to use what's used on screen or on official sites when it comes to certain punctuation marks, because in logos and on-screen subtitles parts of titles are usually on different lines, but the line divisions need to be converted to colons and dashes to represent them on one line. And when colons and dashes are used, which is used where is often not consistent and up to the whims or policies of whoever's formatting the title for that particular use.

In this case, what character is used where and how the title is capitalised are quite consistent, but even in these cases there's the question of which character to use for dashes, as though there are Unicode characters for en (–) and em (—) dashes their existence is extremely neglected by the general English-speaking public and the cinema and TV industry (though newspaper/book publishing doesn't have a problem with using them, at least in macOS one only needs to hold down alt and press hyphen to type an en dash, and with mobile OSes only needs only to hold down the hyphen key and slide over to the correct dash).

It's a similar case as to whether to use the specific apostrophe, quotation mark and prime characters (which TMDb can use because it's in Unicode) or the generic multi-purpose ones (though not exactly; which apostrophes and quotation marks to use is case of stylisation, whereas hyphens, en dashes and em dashes have different meanings and call for different spacing around them). I've learnt from the forum that the latter is preferred (despite the former being possible), but I don't think that's in the bible, either? That said, since these punctuation rules would apply to titles, synopses and other text, and across movies and TV, I'm not sure where they would go.

All of which of which is a site-wide enough issue to to deserve at least its own thread, so I won't derail this one any more, though it's this title which has led to me bringing that up.