Use your own Intl-Resources with ResourceBundle

Code
<?php

// Resources: http://bugs.icu-project.org/trac/browser/icu/trunk/source/data/curr
// res-files created with genrb
$resource = __DIR__ . '/resources';

// italian locale, returns null on error
$curr = new ResourceBundle('it', $resource);

// get old german currency
$demCurrency = $curr->get('Currencies')
    ->get('DEM');

echo $demCurrency->get(0) . PHP_EOL;
echo $demCurrency->get(1) . PHP_EOL;

// no error happened
echo 'ErrorCode: ' . $curr->getErrorCode() .
    ', ErrorMessage: ' . $curr->getErrorMessage();
Result
DEM
Marco Tedesco
ErrorCode: 0, ErrorMessage: U_ZERO_ERROR
Used Versions
PHP 8.3, Laminas MVC 3.2, Symfony 5.2, Laravel 8.28, PHPUnit 9.5, Doctrine ORM 2.8