CLDR-18855 Clarify regional locale formatting expectations (#4908)

Co-authored-by: Fredrik <[email protected]>
Co-authored-by: Mark Davis <[email protected]>

Author: 3 people

docs/site/translation/number-currency-formats/number-symbols.md

@@ -6,7 +6,17 @@ title: Number Symbols
 
 The following symbols are used to format numbers. The Approved symbols for the locale will be substituted for the placeholders described in [Number Patterns](/translation/number-currency-formats/number-and-currency-patterns). 
 
-For English regional locales (e.g. en\_DE) where English is not the primary language of the country/region (e.g. en\_DE; English as used in Germany), the number formats and date formats should follow the **English formatting usage** in that country/region. Often, the formatting usage in English tend to follow the British or American formatting rather than the formatting of the primary language. Consult with the English versions of prominent magazines or newspapers for guidance on date and number format usage.
+For regional locales where the language is not the primary language of the country/region (e.g. en\_DE, English as used in Germany; or es_SE, Spanish as used in Sweden), there are different possible options for the number formats and date formats.
+As with other CLDR data, the most customary form of _that_ language as used in _that_ country should be followed.
+This is generally one of two options (or something in between):
+
+1. The conventions of one of the main regional variants (e.g. en\_GB), such as 1,234.5 or 21/02/2025 or 21 February 2025
+2. The conventions of one of the main languages used in the country, such as 1’234,5 or 2025-21-01 or 21. February 2025
+
+The choice of which option is most customary can be difficult to determine with languages that are operating as a lingua franca for people who don't have it as their first language.
+In these situations, much of the available content is written for an international audience and most of the readers are from other countries/regions.
+
+Developers can choose a specific language variant, such as en\_GB, with a specific region's formatting by using [the Region Override U extension](https://www.unicode.org/reports/tr35/#RegionOverride) if they, for example, prefer British English formatting in a region/country with different number or date formatting.
 
 | Name | English Example |  | Meaning |
 |---|---|---|---|