Index: typo3/classes/class.typo3ajax.php
===================================================================
--- typo3/classes/class.typo3ajax.php	(Revision 5596)
+++ typo3/classes/class.typo3ajax.php	(Arbeitskopie)
@@ -248,9 +248,15 @@
 	 * @return	void
 	 */
 	protected function renderAsJSON() {
+			// if the backend does not run in UTF-8 then we need to convert it to unicode as
+			// the json_encode method will return empty otherwise
+		if ($this->charset != $this->requestCharset) {
+			$GLOBALS['LANG']->csConvObj->convArray($this->content, $this->charset, $this->requestCharset);
+		}
+
 		$content = json_encode($this->content);
 
-		header('Content-type: application/json; charset='.$this->charset);
+		header('Content-type: application/json; charset='.$this->requestCharset);
 		header('X-JSON: '.($this->contentFormat != 'jsonbody' ? $content : true));
 
 			// bring content in xhr.responseText except when in "json head only" mode