private function handlePrependLocale(array $extensionConfigs, ContainerBuilder $container): array
    {
        if (!$container->hasParameter('prepend_locale')) {
            return $extensionConfigs;
        }

        foreach ($extensionConfigs as $extensionConfig) {
            if (isset($extensionConfig['prepend_locale'])) {
                return $extensionConfigs;
            }
        }

        @trigger_error('Defining the "prepend_locale" parameter in the parameters.yml file has been deprecated and will no longer work in Contao 5.0. Define the "contao.prepend_locale" parameter in the config.yml file instead.', E_USER_DEPRECATED);

        $extensionConfigs[] = [
            'prepend_locale' => '%prepend_locale%',
        ];

        return $extensionConfigs;
    }