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.