fetchSimilarLocales: All-lowercase Accept-Language header doesn't work

[cachius]

Safari on MacOS sends an all-lowercase header like Accept-Language: de-de. On case-sensitive filesystems this causes MomentLocale.php::fetchSimilarLocales not finding alternatives.

$dir = dirname($path);
$lang = basename($path);

$locales = glob("$dir".DIRECTORY_SEPARATOR.substr($lang,0,2) . '*.php');

works around that. It would be even better to be also case-insensitive to the first part of the locale.
C.f. Can PHP's glob() be made to find files in a case insensitive manner?