remove abort(); change lang-def de => de-de; cleanup

language.php

@@ -1,7 +1,12 @@
 <?php
-$lang = "de";
+$lang = "de-de";
 if(isset($_GET['lang'])){
-	$lang = $_GET['lang'];
+	$lang = filter_var($_GET['lang'], FILTER_SANITIZE_STRING);
 }
-require_once("lang/lang.".$lang.".php");
+$lang_file = "lang/lang.".$lang.".php";
+if (!file_exists($lang_file)) {
+	throw new Exception("Translation for " . $lang . " not found");
+}
+require_once($lang_file);
+unset($lang_file);
 ?>