My OS locale is set up for English language, but continental dates, numbers, metric units and currency. Writer does not understand this and imposes its own measurement units etc. apparently based only on the language selected.
I’ve verified this under Tools .> Options → Language Settings.
How do I get LO to use the system-wide locale settings instead of its own language/locale settings?
Alternatively: how can I change Writer unit/monetary/decimal settings?
Thank You.
I think you have to change the settings for LO
Units: Tools > Options > LibreOffice Writer > General under Measurement unit set Millimeter
Decimal and dates you could change your locale in Tools > Options > Language Settings, Swedish (Sweden) is the first one I saw that has Y-M-D if that is what is meant by Continental date and has decimal comma instead of decimal point. Make sure your Default Language for Documents is the English variation you prefer
Setting Currency doesn’t work for Writer tables, there it is the language of the document, e.g. English UK will be Pounds, USA will be $. It does work for Calc so you could embed a Calc “table” in a Writer document
Some will disapprove of these settings but I see no reason why you couldn’t be in Sweden writing documents in English UK for a Swedish company; my brother-in-law does.
Thank You for your reply.
Yes, apparently LO maintains its own language/locale settings. I tried your suggestion, and it works. What’s now left for me is maintaining system locale settings and LO locale settings and other locale settings. Sigh! It could have been so easy, but I’ll live with it as it is.
Thanks again 
At least LO retains its settings regardless of OS vagaries. If you had Windows you would have a lifetime of changing OS settings back from USA with each update, although LO would be OK.
Sorry this is not correct. In Windows one can set date, time, currency formats, independently of language and country and most program respect the settings (not LO alas.) And those settings are preserved across system updates(even major OS updates.)
The whole locale system is broken in Linux and more so in LO : living in a multilingual country, using different languages and having more or less valid country format settings imposed is not very ergonomic. And in Linux installing language packs will confuse a lot of programs, even system programs ! On a Debian 11 I have seen some programs using two different languages in their interface while the LANG and LANGUAGE locale settings were set to en-UK.
All programs should use the different system settings for formats ans son on as a default, then one can offer to use different settings for the program, or for a particular document.
That one can select a country to set the individual settings is a good thing. But programs should only use the individual settings not assume them based on a country (especially since different programs and OSes have different opinions about what the settings are !) One can live in one country, use the language of another to write documents using settings from no existing country. Since most countries are multilingual this problem will be more acute over time.
Thanks for disrespecting my lived experience over many years, updates and computers, including entire office worth.
Do you have a question? or do you want to file an enhancement, How to Report Bugs in LibreOffice - The Document Foundation Wiki
There is already long standing tdf#46448.
I am sorry to have caused you distress. My experience is different from yours. No disrespect intended.
(Not LO but to illustrate the difficulty of basing settings on a country : I just did two installation of Debian, the cinnamon version has no easy way for changing the individual locale settings, the KDE version has but uses a different date and time format for en-DK.UTF-8 than other Linux flavours !)
(I also saw that for some the UK has already reverted to imperial or perhaps never changed to metric.)
To come back to LO, I found no easy way to have English for the interface but with metric units, date and time in ISO formats, EUR for currency, comma and space as decimal and thousands separator, French collating order, … I could try to edit locale.py to get what I want, but it would be a hack, and I would have to redo this at each LO update or installation.
What a lot of people wish is the possibility to use the system settings or, if the programming should be independent of the OS, to be able to set the different settings independently of a country. And, it would be great to be able to use different settings for a document.
But it is indeed related to tdf#46448.
Again my sincere apologies for having caused you to feel disrespected.
Fwiw, since LibreOffice 7.2 there is the en-DK locale you could choose under Language Settings, see LibreOffice 7.2 Community: Release Notes - The Document Foundation Wiki .