Steps to reproduce the issue

Arrange for an extension update site to have an invalid URL (eg. temporarily mangle the URL in the extensions database). Then run
php cli/joomla.php update:extensions:check from the command line.

Expected result

Warning message something like
[WARNING] Update: Could not open update site #4 "xxxxxxxxxxx Package Update Site", URL: https://example.com/xxxxx/update.xml

Actual result

[WARNING] JLIB_UPDATER_ERROR_OPEN_UPDATE_SITE

System information (as much as possible)

Joomla 4.4.3
PHP 8.1

Additional comments

The string exists in administrator/language/en-GB/lib_joomla.ini and language/en-GB/lib_joomla.ini so the problem is that the language file is not being loaded at the appropriate time.