The default decimal separator key for South Africa is wrong.
South Africa uses dot notation and not comma notation.
Solution : Goto Tools, Options, Language Settings, Languages
Keep user interface Default - English USA
Change Local Settings from default to any country with dot separator
(I used Dzonghkha)
Then go down to Default Currency and change it back to ZAR.
And change your date settings back to Y-M-D;Y/M/D;M-D;M/D
Apply or Save and all is well!
(I did this on Libre Office 6.4.4)
It appears that Libre has an option for decimal separator “same as locale”, but this didn’t appear to do anything. (I’m also from SA and recently switched from Open to Libre, don’t know how long this has been there or how long it’s been an issue).
In defence of the period/dot/. - when using the keypad, the thing next to zero is a dot, not a comma. Importing CSV’s with decimals needs to be preprocessed first to first use something other than a comma as the variable separator, then use the comma as the decimal separator. All of this is just so archaic, I’m sure the last people in SA that used a comma as a decimal separator were accountants in the 80’s.
I completely understand having the default set to the locale standard, but there should be some easier way to get around the problem to switch to the dot than modifying Dzongkha. Perhaps make the “Decimal separator key” option actually do something?
The default decimal separator key for South Africa is wrong. South Africa uses dot notation and not comma notation.
No, it is incorrect statement.
Official separator in en-ZA is comma. Dot is indeed widely used; and users in the country might even be unaware of their standards; but the facts are mentioned in tdf#119613 (which changed from dot to comma) and tdf#127602 (which asked to do the opposite, and was closed WONTFIX).
If you want dot to become official standard in the country, you need to act on a different level 
I humbly apologize.
I had a look, and it is true! South Africa does use the comma!
As stated in this in-depth article by Robert MacLean on Fri, 09/28/2012
https://www.sadev.co.za/content/how-correctly-format-currency-south-africa
Which quote this pdf: http://www.eepublishers.co.za/images/upload/PostionIT%202011/PositionIT_April_May_2011___SurvT_The%20SA.pdf
However, in my 55 years here in South Africa I have not seen anyone use commas in spreadsheets 
Don’t worry.
All the continantal Europe, e.g. is using the comma as the decimal seoarator.
All of it?
No. There is Liechtenstein as an exception, and there are a few cantons of Switzerland where the dot is used, and some where it (the dot) is only used for currency amounts. Then -so I was told- pupils are trained to write the dot but to speak the comma.
Human inventiveness is unlimited if it comes to creating nonsense and useless complications,
Even ISO couldn’t pull off a single decimal separator for the world in times of Unicode. They accept both variants in use, but explicitly deprecate the comma and the point as well for usage as a group separator - well knowing that nobody will obey this rule…
Unicode, however, introduced a DECIMAL SEPARATOR KEY SYMBOL with place U+2396 (hex), They made sure that nobody will use it by (among other tricks) making it the ugliest glyph ever.
You know? We need to create Artificial Intelligence because there isn’t NI.
The official South African standard decimal separator is a comma.
This was determined in about 1970 and was supposedly based on some European metrication standard.
Computer use in 1970 was mostly limited to a few mainframe systems, so the decision to use a comma probably did not even consider computing aspects, but was to ensure clear recognition of the decimal separator in handwritten text.
In retrospect it was not a good decision, and probably beyond understanding to change it now.
The use of the point (period) as a decimal separator is now so widespread in computing (certainly in Western languages) and especially in engineering software, that using a comma just creates frustrating inconsistencies.
Libre Office should ingore the old SA standard and use a point as the local SA default, or at least allow the option to change it at installation time.
Otherwise the spreadsheets cannot be used together with all the other software (database, accounting, engineering, cad etc). And the decimal on the number keypad only produces a point character.
I dont know how we can get Libre Ofice to correct the problem.
Some forum suggestions that users in SA should set their locale as UK and then set the currency back to Rand might work but it is not logical.
Funny how so many other locales happily use comma and don’t experience those severe problems that you declare here. We in Russia is one example; many European countries is another. I suppose that in fact, what you describe is not a fundamental flaw, but just a problem of two different de-facto standards used side by side in the same country. Having standardize on any single one of these would be equally convenient, and I doubt that decimal dot (or decimal comma) has any actual fundamental benefit over the other by itself, only habits matter.
Libre Office should ingore the old SA standard
A stupid suggestion. A standard is a standard and should be followed (when, of course, it is still valid). The fact that South Africans do not follow their own standard is stupid, too. A stupidity is not a remedy against another stupidity, it just multiplies issues.
LibreOffice is generally about a standard, namely ODF. Result: documents in ODF open happily in Apache OpenOffice and in any other program that follows the standard. That’s the power of standardization.
Take Microsoft: they don’t follow even the standard that they pushed (OOXML), only some undisclosed specifications. Result: documents created in some version of Microsoft Office may open with faults in another version.