Any addition of an UI language would require a redesign of the DB table "questiontype". I.e. adding a column.
For example.
		CREATE TABLE `questiontype` (
		  `qt_id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'Fragetypenschlüssel',
		  `DE` varchar(25) COLLATE latin1_general_ci NOT NULL DEFAULT '' COMMENT 'Fragetyp',
		  `EN` varchar(25) COLLATE latin1_general_ci NOT NULL DEFAULT '',
+		  `NL` varchar(25) COLLATE latin1_general_ci NOT NULL DEFAULT '',
		  PRIMARY KEY (`qt_id`)
		) ENGINE=MyISAM AUTO_INCREMENT=5 DEFAULT CHARSET=latin1 COLLATE=latin1_general_ci COMMENT='Fragetypen'
	
I've redefined the table as
		CREATE TABLE `questiontype_v2` (
		  `qt_id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'Fragetypenschlüssel',
		  `lang` varchar(5) COLLATE latin1_general_ci NOT NULL DEFAULT '' COMMENT 'Sprache',
		  `qt_desc` varchar(25) COLLATE latin1_general_ci NOT NULL DEFAULT '' COMMENT 'Fragetyp',
		  PRIMARY KEY (`qt_id`,`lang`)
		) ENGINE=MyISAM AUTO_INCREMENT=5 DEFAULT CHARSET=latin1 COLLATE=latin1_general_ci COMMENT='Fragetypen'
Which lets you add rows for each language you want.
The new table is quickly prefilled using:
	INSERT INTO questiontype_v2 select qt_id, 'DE' AS lang, DE AS qt_desc FROM questiontype
	INSERT INTO questiontype_v2 select qt_id, 'EN' AS lang, EN AS qt_desc FROM questiontype

I've upgraded both of the functions dealing with this table.
I've also taken the liberty to use sprintf. This way it's a bit easier to see what is in the query to be executed.

CATS/database/create_db.sql has yet to be updated.


Index: classes/Question.class.php
===================================================================
--- CATS/classes/Question.class.php	(revision 1641)
+++ CATS/classes/Question.class.php	(working copy)
@@ -179,7 +179,7 @@
     
    function returnTypeName($type){
   // if($type==0)$type=$_SESSION ['values']['question']['qt'];
-   $sql="SELECT ".mysql_real_escape_string($_SESSION['profile']['language'])." as type FROM questiontype WHERE qt_id='".intval($type)."'";
+   $sql=sprintf("SELECT qt_desc as type FROM questiontype_v2 WHERE qt_id='%d' AND lang='%s'", intval($type), mysql_real_escape_string($_SESSION['profile']['language']));
    $query = mysql_query($sql);
    $type = mysql_fetch_assoc($query);
    $this->typeName="321 ".$type['type'];
--- CATS/functions/showQuestionForm.php	(revision 1641)
+++ CATS/functions/showQuestionForm.php	(working copy)
@@ -30,7 +30,7 @@
       echo"<td class='left_point'> :  </td>";
       echo "<td class='text'>123 ";
       
-      $sql_qtypes ="SELECT qt_id, ".mysql_real_escape_string($_SESSION['profile']['language'])."  as type FROM questiontype "; 
+      $sql_qtypes=sprintf("SELECT qt_id, qt_desc as type FROM questiontype_v2 WHERE lang='%s'", mysql_real_escape_string($_SESSION['profile']['language']));
       $query_qtypes = mysql_query($sql_qtypes) or die(mysql_error()); 
       
         if($_SESSION['values']['question']['qt']==null && $error=='missing')echo"<select size='1' class='dropdown_right marked' name='qt' > ";