Gettext not translating PHP in Debian 10

I’m trying to localize my website, it is located in a VPS running LEMP Debian 10 (PHP 7.3.27-1~deb10u1). I have spent the day troubleshooting why it’s not working with no success.

My project has the following structure:

MY_PROJECT_NAME
   - locale
       - en_GB
            LC_MESSAGES
               en_GB.mo
               en_GB.po
       - es_ES
            LC_MESSAGES
               es_ES.mo
               es_ES.po
   - index.php

The file index.php has the following code:

<?php

session_start();
$language = "es_ES";

if (isset($_GET['language']))
{
    $language = $_GET['language'];
}

putenv("LANG=" . $language);
putenv("LC_ALL={$language}");
setlocale(LC_ALL, $language);

$domain = $language;
bindtextdomain($domain, "./locale/");
textdomain($domain);
bind_textdomain_codeset($domain, 'UTF-8');

var_dump( file_exists("./locale/$language/LC_MESSAGES/$language.mo" ) ); //bool(true) if exists
echo ('<br/>');
echo $language; //output the lang name
echo ('<br/>');
echo gettext('hello'); //text to be translated

?>

The content of file es_ES.po is as follows:

msgid ""
msgstr ""
"Project-Id-Version: n"
"POT-Creation-Date: 2021-05-28 00:19-0500n"
"PO-Revision-Date: 2021-05-28 01:54-0500n"
"Last-Translator: n"
"Language-Team: n"
"MIME-Version: 1.0n"
"Content-Type: text/plain; charset=UTF-8n"
"Content-Transfer-Encoding: 8bitn"
"X-Generator: Poedit 2.4.3n"
"X-Poedit-Basepath: .n"
"Plural-Forms: nplurals=2; plural=(n != 1);n"
"Language: es_ESn"

msgid "hello"
msgstr "Hola mundo"

and the file en_GB.po has the following content:

msgid ""
msgstr ""
"Project-Id-Version: n"
"POT-Creation-Date: 2021-05-28 00:16-0500n"
"PO-Revision-Date: 2021-05-28 01:54-0500n"
"Last-Translator: n"
"Language-Team: n"
"MIME-Version: 1.0n"
"Content-Type: text/plain; charset=UTF-8n"
"Content-Transfer-Encoding: 8bitn"
"X-Generator: Poedit 2.4.3n"
"X-Poedit-Basepath: .n"
"Plural-Forms: nplurals=2; plural=(n != 1);n"
"Language: en_GBn"

msgid "hello"
msgstr "Hello word"

Both files has been compiled with POedit, to generate the correct .mo files.

Also, i have added the locales to the system via sudo dpkg-reconfigure locales. The output of the command locale -a is the following:

C
C.UTF-8
de_DE.utf8
en_GB.utf8
en_US.utf8
es_ES.utf8
it_IT.utf8
ja_JP.utf8
POSIX
pt_BR.utf8

Whenever i run the php code to check if the translation works:
index.php?language=en_GB
index.php?language=es_ES

I get the output:

bool(true)
en_GB
hello

and

bool(true)
es_ES
hello

Respectively. What am i missing? There is no error in the logs, i have rebooted the server to makie sure it’s not a cache issue, also i have tried several variants of the index.php configurations with no success.