Regional Formats, create my own, covering ALL, how?

Question

Is there a single easy option to have an "International" Region/Language option?

e.g. I wish to have a DATE format as indicated by these...

$ date --rfc-3339=date
2022-10-10

$ date --iso-8601=date
2022-10-10

$ date --rfc-3339=seconds
2022-10-10 16:22:55+02:00

$ date --iso-8601=seconds
2022-10-10T16:23:06+02:00

$ 

Time should ALWAYS be "24h", skip that pesky AM/PM.

Numbers; decimal POINT, and possibly space as thousands separator.

Ref:
How do I enter dates in ISO 8601 date format (YYYY-MM-DD) in Excel (and have Excel recognize that format as a date value)?
How to make date YYYY-MM-DD (ISO-8601) the default in Excel?
... and probably more, similar.

Answer 1

---

---

The name of your locale has to be stated in either
/etc/locale.gen
-or-
/usr/share/i18n/SUPPORTED

---

---

In the end, the number grouping symbol actually already was set to Narrow-Non-Break-Space <U+202F>, didn't have to change that (I have seen , in use at some point, can't remember when).

The use of , (comma) as decimal marker was present though, both in monetary and general number format specifications; I replaced that with the more "versatile" . (period). So, the sequence of commands... and use of the nano editor for the changes:

$ cp /usr/share/i18n/locales/sv_SE sv_SE_nerdy

$ nano sv_SE_nerdy 

$ diff -bu0 /usr/share/i18n/locales/sv_SE sv_SE_nerdy 
--- /usr/share/i18n/locales/sv_SE   2022-04-07 03:24:41.000000000 +0200
+++ sv_SE_nerdy 2022-10-21 22:22:00.321168816 +0200
@@ -182 +182 @@
-mon_decimal_point       ","
+mon_decimal_point       "."
@@ -198 +198 @@
-decimal_point           ","
+decimal_point           "."
@@ -276 +276 @@
-lang_name    "svenska"
+lang_name    "svenska, decimalpunkt"

$ sudo cp sv_SE_nerdy /usr/share/i18n/locales/

$ sudo locale-gen

$ localectl set-locale LC_MONETARY=sv_SE_nerdy

$ localectl set-locale LC_NUMERIC=sv_SE_nerdy

NOTED FAULT: The monetary format (as specified above) is not used in LibreOffice Calc 6.4.7.2, or is it just dependent on selecting it? Using English as Language during testing.