Multi language error handling for TYPO3 & RealURL

AdditionalConfiguration.php

<?php

$GLOBALS['USER']['vendorname']['domainConfigurations'] = array(
	'domain.tld' => array('rootpageUid' => 1, 'languages' => array('en' => 1)),
);

realurl_conf.php

<?php

// ...

if (isset($_SERVER['REQUEST_URI']) && isset($_SERVER['HTTP_HOST'])) {
	$languageKey = substr($_SERVER['REQUEST_URI'], 1, 2);
	if (array_key_exists($_SERVER['HTTP_HOST'], $GLOBALS['USER']['vendorname']['domainConfigurations'])) {
		$configuration = $GLOBALS['USER']['vendorname']['domainConfigurations'][$_SERVER['HTTP_HOST']];
		if (array_key_exists($languageKey, $configuration['languages'])) {
			$TYPO3_CONF_VARS['FE']['pageNotFound_handling'] = $languageKey . '/' . $TYPO3_CONF_VARS['FE']['pageNotFound_handling'];
		}
	}
}