What value for locale should I use on my server?

[torvista]

So, as I was saying earlier (https://www.zen-cart.com/showthread....l-server-maybe),
it may sometimes be a real headache to know what to put in your main language file (the equivalent of english.php) for this

  $locales = array('en_US', 'en_US.utf8', 'en', 'English_United States.1252'); 

so that you do not get character set/encoding issues.

As I develop on Windows/Xampp, the php-generated day names in spanish are displayed with corrupted characters where the accent should be
eg.: s�bado 23 diciembre 1978,
a typical encoding problem that can often be seen on the interweb, and usually easily fixed with a bit of care.

Using setlocale(LC_ALL, $locales); instead of LC_TIME
and adding
ini_set('default_charset', "UTF-8");
to php.ini
do not fix this problem, which I think is not fixable.
It seems Windows cannot produce these utf-8 things as mentioned here:

"The locale argument can take a locale name, a language string, a language string and country/region code, a code page, or a language string, country/region code, and code page. The set of available locale names, languages, country/region codes, and code pages includes all those supported by the Windows NLS API except code pages that require more than two bytes per character, such as UTF-7 and UTF-8.
If you provide a code page value of UTF-7 or UTF-8, setlocale will fail, returning NULL."

So, the only solution I found was to convert the result in function zen_date_long to utf-8 only for Windows as shown here

    return ( stristr(PHP_OS,"win") ? 
    utf8_encode(strftime(DATE_FORMAT_LONG, mktime($hour, $minute, $second, $month, $day, $year))) : 
    strftime(DATE_FORMAT_LONG, mktime($hour, $minute, $second, $month, $day, $year)) );  
  } 

I spent/wasted hours down this particular rabbit-hole and wrote a script to identify what values for locale you could use on your particular server. I also added a few links to the most useful references I found on the topic and a way to list all installed locales on a Windows computer (added here for googlers), so here it is for your delight:
test_locales.zip