I have a LO document that I edit using Nextcloud with ~10 other people who are based in different locations. Sometimes at the same time. I recently hit a problem where someone with a different locale from me opened the document first and as a result, the equations that I was putting into the document (and possibly some of the existing ones) didn't work. (Our locales have different decimal separators.) As a user, I don't want to have to check the locale every time I open a document via the online editor. I would like to be able to set the locale for a document to always use when it is being edited online, regardless of the user's locale as a variable locale for everyone is more inconvenient that a fixed one which is not the right one for some users. I think that there should a setting in the document preferences to specify the locale for that document when it is being edited online. When the document is being edited offline with the desktop LO app, the document should continue behaving as it does now and using the user's locale. I think it would make sense for this setting to only be visible when a document is open via the Nextcloud app.
Confirmed, thanks for reporting, Kat. As a bit of additional explanation, the locale is decided when a session is launched, and is currently based on that user's language settings/locale in the integration. A document-specific locale is a bit alien, but might be the most straightforward solution. Most of this feature would have to be developed on the integration side. While it doesn't help here, Nextcloud 14 has separate user language and locale settings (could help if the collaborating users set the same locale, while they can have separate user interface languages, but this setting isn't taken into account, yet).