Loading localized labels for JavaScript with TYPO3 Flow/Fluid

JavascriptLabelsViewHelper.php

<?php
namespace Cobweb\Monitoring\ViewHelpers;

/*                                                                        *
 * This script belongs to the FLOW3 package "Cobweb.Monitoring".          *
 *                                                                        *
 * It is free software; you can redistribute it and/or modify it under    *
 * the terms of the GNU Lesser General Public License, either version 3   *
 *  of the License, or (at your option) any later version.                *
 *                                                                        *
 * The TYPO3 project - inspiring people to share!                         *
 *                                                                        */

use TYPO3\FLOW3\Annotations as FLOW3;

/**
 * Takes some localized strings and makes them available in JavaScript
 *
 * IMPORTANT: note that that the string keys must not contain dots (.) or dashes (-)
 * as JavaScript will choke on them.
 *
 * = Examples =
 *
 * <code title="JavaScript labels">
 * <monitoring:javascriptLabels keyList="{0: 'yourFather'}" source="EmpireStrikesBack" package="StarWars"></monitoring:javascriptLabels>
 * </code>
 * <output>
 * <script type="text/javascript">
 * var Language = {
 * yourFather: 'Luke, I\'m your father.',
 * };
 * </script>
 * </output>
 *
 * @api
 */
class JavascriptLabelsViewHelper extends \TYPO3\Fluid\Core\ViewHelper\AbstractViewHelper {

	/**
	 * @var \TYPO3\FLOW3\I18n\Translator
	 * @FLOW3\Inject
	 */
	protected $translator;

	/**
	 *  Reads some localized strings and stores them in global JS array
	 *
	 * This makes these strings usable from JavaScript
	 * Much code taken from \TYPO3\Fluid\ViewHelpers\TranslateViewHelper
	 *
	 * @param array $keyList List of strings to fetch
	 * @param string $source Name of file with translations
	 * @param string $package Target package key. If not set, the current package key will be used
	 * @param string $locale An identifier of locale to use (NULL for use the default locale)
	 * @throws \TYPO3\Fluid\Core\ViewHelper\Exception
	 * @return string A <script> tag containing the localized labels, as properties of a global object
	 * @api
	 */
	public function render(array $keyList = array(), $source = 'Main', $package = NULL, $locale = NULL) {
		$localeObject = NULL;
		if ($locale !== NULL) {
			try {
				$localeObject = new \TYPO3\FLOW3\I18n\Locale($locale);
			} catch (\TYPO3\FLOW3\I18n\Exception\InvalidLocaleIdentifierException $e) {
				throw new \TYPO3\Fluid\Core\ViewHelper\Exception('"' . $locale . '" is not a valid locale identifier.' , 1279815885);
			}
		}
		if ($package === NULL) {
			$package = $this->controllerContext->getRequest()->getControllerPackageKey();
		}

		$content = '<script type="text/javascript">';
		$content .= 'var Language = {' . "\n";
		foreach ($keyList as $key) {
			$translation = $this->translator->translateById($key, array(), NULL, $localeObject, $source, $package);
			$content .= $key . ': ' . "'" . addslashes($translation) . "',\n";
		}
		$content .= '};' . "\n";
		$content .= '</script>';
		return $content;
	}
}

?>

Btw this code is likely vulnerable to XSS if malicious localizations would be used. The strings could include </script>.
Edit: The addslashes might prevent it, but I wouldn't be sure about it. Better use something safer.