U_illegal_argument_error

This is happening on multiple Zen Cart sites. All seem to be ZC 1.5.8 and PHP 8.x

PHP Fatal error: Uncaught IntlException: datefmt_create: invalid locale: U_ILLEGAL_ARGUMENT_ERROR in /XXXXXX/includes/classes/zcDate.php:87

I saw a thread about this error and PHP 8.3 on GitHub, but see no mention in this forum.

So it's happening with PHP 8.1 and 8.2, 8.0 is ok.

Affects 8.1.25, 8.2.12, and 8.3.0RC3+

Ongoing discussion at: Site Crashed U_ILLEGAL_ARGUMENT_ERROR