Index: t3lib/config_default.php
===================================================================
--- t3lib/config_default.php	(revision 5852)
+++ t3lib/config_default.php	(working copy)
@@ -168,6 +168,7 @@
 		'extConf' => array(						// Config-options for extensions, stored as serialized arrays by extension-keys. Handled automatically by the EM.
 //			'--key--' => array()
 		),
+		'locallangXMLOverride' => array(),					// For extension/overriding of the arrays in 'locallang' files in frontend and backend. See 'Inside TYPO3' for more information.
 	),
 	'BE' => Array(		// Backend Configuration.
 		'unzip_path' => '',						// Path to "unzip".
Index: t3lib/class.t3lib_div.php
===================================================================
--- t3lib/class.t3lib_div.php	(revision 5852)
+++ t3lib/class.t3lib_div.php	(working copy)
@@ -4315,6 +4315,13 @@
 			} else {
 				die('File "' . $fileRef. '" not found!');
 			}
+			if (isset($GLOBALS['TYPO3_CONF_VARS']['EXT']['locallangXMLOverride'][$fileRef])) {
+				$languageOverrideFileName = t3lib_div::getFileAbsFileName($GLOBALS['TYPO3_CONF_VARS']['EXT']['locallangXMLOverride'][$fileRef]);
+				if (@is_file($languageOverrideFileName)) {
+					$languageOverrideArray = t3lib_div::readLLXMLfile($languageOverrideFileName, $langKey, $charset);
+					$LOCAL_LANG = t3lib_div::array_merge_recursive_overrule($LOCAL_LANG, $languageOverrideArray);
+				}
+			}
 		}
 
 		return is_array($LOCAL_LANG) ? $LOCAL_LANG : array();
Index: typo3/sysext/cms/tslib/class.tslib_pibase.php
===================================================================
--- typo3/sysext/cms/tslib/class.tslib_pibase.php	(revision 5852)
+++ typo3/sysext/cms/tslib/class.tslib_pibase.php	(working copy)
@@ -970,7 +970,7 @@
 	 */
 	function pi_loadLL()	{
 		if (!$this->LOCAL_LANG_loaded && $this->scriptRelPath)	{
-			$basePath = t3lib_extMgm::extPath($this->extKey).dirname($this->scriptRelPath).'/locallang.php';
+			$basePath = 'EXT:' . $this->extKey . '/' . dirname($this->scriptRelPath) . '/locallang.xml';
 
 				// Read the strings in the required charset (since TYPO3 4.2)
 			$this->LOCAL_LANG = t3lib_div::readLLfile($basePath,$this->LLkey,$GLOBALS['TSFE']->renderCharset);