Viewing a page with country code causes infinit redirect then error 500.

What specifically are the “location” HTTP headers? What exactly is the 500 error logged?

Dev env log:
php-error ded-47001 [15-Mar-2024 13:37:20 Europe/London] PHP Fatal error: Aborting! The New Relic imposed maximum PHP function nesting level of '5000' has been reached. This limit is to prevent the PHP execution from catastrophically running out of C-stack frames. If you think this limit is too small, adjust the value of the setting newrelic.special.max_nesting_level in the newrelic.ini file, and restart php. Please file a ticket at https://support.newrelic.com if you need further assistance. in /mnt/www/html/cambunipressloadtest/docroot/modules/contrib/key/src/KeyConfigOverrides.php on line 115 request_id="v-25d327a4-e2d1-11ee-8002-cbe2c8d7752a"

Localhost log:
Only in this error that there is no log showing

Already have this:
error_reporting(E_ALL);
error_reporting(-1);
ini_set('error_reporting', E_ALL);
set_time_limit(0);
ini_set('memory_limit','2048M');

$config['system.logging']['error_level'] = 'verbose';

Response header:

Age:
0
Content-Length:
0
Content-Type:
text/html; charset=UTF-8
Date:
Fri, 15 Mar 2024 13:37:20 GMT
Server:
nginx
Via:
varnish
X-Ah-Environment:
env-name
X-Cache:
MISS
X-Request-Id:
v-25d327a4-e2d1-11ee-8002-cbe2c8d7752a

Response preview:
Failed to load response data. No resource with given identifier found.

Request header

:authority:
env-url-here
:method:
GET
:path:
/us/nodealias
:scheme:
https
Accept:
text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7
Accept-Encoding:
gzip, deflate, br, zstd
Accept-Language:
en-GB,en-US;q=0.9,en;q=0.8
Cache-Control:
max-age=0
Cookie:
locale=en_US; preferredCountry=US; preferredLocale=en_US; other cookies
Sec-Ch-Ua:
"Chromium";v="122", "Not(A:Brand";v="24", "Google Chrome";v="122"
Sec-Ch-Ua-Mobile:
?0
Sec-Ch-Ua-Platform:
"Windows"
Sec-Fetch-Dest:
document
Sec-Fetch-Mode:
navigate
Sec-Fetch-Site:
none
Sec-Fetch-User:
?1
Upgrade-Insecure-Requests:
1
User-Agent:
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.0.0 Safari/537.36

This issue says that this is a redirect bug but the HTTP response has no location header. How did you conclude this involves redirects?

Is xdebug enabled?

This bug report needs very clear steps to reproduce that begin with installing Drupal.

After further investigation this is cause by by custom _language_fallback_candidates_alter hook that call getPathByAlias.
The hook_language_fallback_candidates_alter is being called infinitely resulting in memory exhaustion.