How to set system Short Date to ISO format "yyyy-MM-dd" in High Sierra?

I think I found the answer myself (at least I have what I want):

My problem: day of month missing trailing zero

System Preferences... > Language & Region > Advanced... > Dates

What I expected was the option to open the Day of Month drop down and select an option with a trailing zero, just as the digit Month allows:

Month digit drop down shows with and without trailing zero

But I don't see that:

trailing zero missing from Day of Month

So when my Googling came up empty, I coincidentally copied the contents of the Short field

short date field

into a text editor and this is what I found:

y-MM-d

So I got the bright idea of pasting "yyyy-MM-dd" into the Short date field and seeing what happens. Sure enough, worked like a charm:

trailing zero in day of month

This also worked with getting the trailing zeros in Excel on the year:

Before:

Awful y-MM-d date format in Mac Excel 2011

After:

ISO "yyyy-MM-dd" date format in Mac Excel 2011

Use/copy the Swedish locale for date and time. It follows the ISO-standard.

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