Let’s make the MB guidelines clear (again):
Unintentional misspelling is mainly due to ignorance and/or fat fingers, and doesn’t count as artist’s intent.
Intent has to be proven.
For the sake of MB database consistency, sticking to commonly accepted spelling (=dictionaries) is much better than editor’s own “preference”.
If an artist writes “acappella” in all places where they talk about this (websites, microblogs, social media, release metadata), does that then count as artist intent? I’d personally say that it does. Maybe the artist doesn’t know any better, but nevertheless, this is how they spell this particular phrase.
MusicBrainz should (IMO) be descriptive, not prescriptive. If people are (esp. consistently) writing certain words or phrases in a certain way, MusicBrainz should mirror that.
If the artist consistently uses “a cappella” but in one instance writes “acappella”, then sure, fix it, since then it’s an obvious typo.
I don’t agree with relying on dictionaries or external sources as a rule (they can be useful to fall back on in some cases) since they, too, are descriptive, not prescriptive (at least with regards for spelling), so they change over time and never fully reflect current usage. (It takes time for a new word or a changed spelling to gain wide enough adoption for it to be notified by dictionary editors and then it needs editing and so on before it finally shows up in a dictionary.) This means that we may change something for a release tomorrow that may not be correct according to current dictionary, but may be correct according to the same dictionary’s edition a couple of years from now. Better to just have it as‐stated from the get‐go.
Yes. If it is not spoken/written/used in the context of your language, then your language is not of significant importance for how it should be used. Language is migratory and adaptive. This phrase has been picked up by the English “diaspora” and been adopted into this language. This adoption frees it from the ‘rules’ of its source/origin language. I mean, you’re using French punctuation even when writing English, so you’re already not following English grammar ‘rules’, and no one’s shouting at you for it… 
@Freso: It looks like I’m alone thinking ignorance cannot be considered as an artist’s intent.
I referred to my language because, in this specific case, etymology says it comes from French/Italian/Latin, I thought it could help to understand why it is a misspelled word. But once again, it seems I’m wrong, since no one cares.
And sorry for incorrect English punctuation, I’ll pay more attention to that in the future, thank you for pointing it out.
I wasn’t aware of this wide ‘adoption’ because most American authoritative sources are describing it as a commonly misspelled word, not as something widely adopted, and no dictionaries are listing this spelling as correct.
I also agree.
Indeed.
Yeah. There are a basic but they are no “rules”. In germany many young people (in other countrys too) create new words. They don’t appear in the dictionaries but if they are spread enough they will (in certain circumstances) get added.
The origin of an word i´will always be there but often these words are getting modified to fit into the language. In this case, the artist wanted to use it in another way. The origin of the word still is there but just a bit different written.
Yeah. I would never do that. I know by myself that i have some/many errors in my messages but i’m not used to write in english. I can read it but writing or speaking it is a bit harder for me.
That is not ignorance. This is a word which is feeling a change. It wouldn’t be the first word. As i wrote above, german words has been changed a lot and still changing to fit the current time. I see it like a word young peoples created.
Nobody says they don’t care. It is just how the current situation is. There a millions songs which are using it and it can’t be ignorred. Sure MusicBrainz could try it but who would that help? No one. It is more work for everyone.
You don’t need to say sorry. I’m learning with it too so you too.
Yes. It isn’t in the dictionaries but i’m sure it could get anytime in it as an synonym. I’m pretty sure sooner or later it will happen. This is how languages are evolving with the time. They need to fit the current time not the past.
As @Freso wrote down:
I do agree too.
Without getting into the semantics, If the artist seems to be meaning to use it that way, “wrong” or “right”, then I would not change it.
Beatport, the biggest digital dance music retailer lists their category for isolated vocal tracks as acapella. I don’t see how this isn’t a “commonly accepted spelling”. It’s been mostly written like this on American dance records since the 80s, compare Discogs which doesn’t “fix” this:
acapella (28,778)
a cappella (10,152)
I don’t see how something that is almost three times as common in print and used by the largest music retailer could be called a typo rather than an anglicization, regardless if it’s in a dictionary or not.
Different languages. Different spellings. “Anglicisation” would refer to making something English as in England, UK. The word you are looking for is “Americanisation”.
Please do not confuse American English with the English that Britain, Canada and Australians speak and write. We are all very different.
Please keep this argument specific to American English and not drag the rest of us into it. Us Brits know them French are hanging out next door,
that’s why we have nicked so much of their language. We use “A Cappella” in the same way as we use many French words.
It is also probably why so many of the Europeans in this thread are also arguing for “correct” spelling.
Americanisation of English has “adjusted the spelling” of many words. This seems to be another one heading into the US Dictionary eventually… but for now, it is clearly miss-spelt as even American’s would correct it.
Note also both your examples of Beatport and Discogs are both American websites.
Though, personally, I don’t see why typos like this can’t be kept on an American cover if an American artist is clearly using it in a consistent manner.
This spelling appears on thousands of records released in the UK, Germany, France, Italy (look at Discogs sidebar) as well, so I’m not sure what your point is. Your attribution of this as an American phenomeon can be instantly disregarded by just looking at those Discogs links. Yes, Discogs is an American website, but their guidelines do not have any standardization of these terms, so it’s completely irrelevant. Even on Italo-disco records, produced, written and released in Italy, the spelling is more common. (The term “a cappella” is Italian)
acapella in track title, filtered by Italy and Italo-disco (54)
a cappella in track title, filtered by Italy and Italo-disco (19)
If it’s considered to be a typo in dance and hip hop music, then why is it three times as common?