How do I enforce decimal character use

I live in South Africa and use the English (South Africa) locale on Windows, but make some changes. Rather than the official decimal separator (comma), thousands separator (space) and list separator (semi-colon) I prefer to use the US standard of period, comma and comma respectively. I have configured my Windows regional settings accordingly and virtually every app I use honours this, but LibreOffice however does not, requiring me to enter the decimal comma.

What do I need to do to ensure that LibreOffice, and particularly Calc, uses the English (South Africa) language for spell checking but the US standards for decimal point, thousands separator and list separator?

Why?
The point and the comma are both deprecated for use as “thousands separator” by international standards. Recommended is “small space”.
In many cases (dates, units, paper sizes…) US standards are specifically bad (stubborn/outdated).
The semicolon as the list separator is clearly superior to the comma because it neither conflicts with the comma nor with the point when used as decimal separator.
Posting formulas with the comma as parameter separator in forums / Q&A sites causes problems again and again.
Never use M/D/Y! It’s a main source of ambiguities in international communication.

Why? You don’t believe in personal choice?
Honestly, i’m happy with thousand separators being space (small big or otherwise) and and list separatorsbbeing semi-colons, but comma as decimal point doesn’t work for me. Largely because there isn’t really a
South African keyboard layout and the majority of our computers have US keyboards, meaning that the
numeric keypad has a decimal point key, not a decimal comma key. So trying to type decimal numbers
one-handed is hardly convenient.

Of course, there are reasons for this or that choice and most of them - in a specific situation - I cannot know. (I don’t know anything about the situation in South-Africa.) Your turn. By the way: I didn’t argue against the “decimal point”. That’s an issue we cannot resolve speedy.
What I try to emphasize now and then is that there are reasons to generally apply international standards - where we have the choice.
Know them, consider them, make an informed choice.
Don’t accept nonsense like the date format used by this Q&A site, e.g.
Concerning group (thousands) separators it’s obvious that there is a conflict. The ISO recommendation is reasonable therefore. It’s also obvious that the recommended “small space” (U+2006 e.g.) isn’t sufficiently supported by LibreOffice.

FYI, here in South Africa we have a slightly strange issue. Although decimal comma, etc. has been official since some time in the 1960s, it wasn’t used in practice. Throughout my school career ending 1979, and my children’s ending mid-2000s we were still taught decimal period, so that was always common use. Then Windows 10 came along using the standard decimal comma, etc. and causing havoc. Even today most people don’t understand why their Excel “breaks” when they open a (US format) CSV file.

Havoc seems to be what everybody aims at.

The odd thing is I checked the en_ZA file and it does correctly use the decimal point not the decimal comma… but libreoffice INSISTS that the system decimal separator is the decimal comma…

Hello,

these 2 settings in Tools -> Options -> Language Settings -> Languages should do what you want:

Thank you, that is exactly what I needed. Have marked if as the accepted answer but am not allowed to upvote due to being new and having no karma.