SCCM2007 Search for WMI SMS_Collection NULL from windows service

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WMI

My environment is Windows Server2008R2(EN) + SQLServer2005(EN) + SCCM2007 SP1(EN).

I use a windows service program to query SMS_Collection for all collections in SCCM. It works fine. But after i change the display language to Deutsch, the query result is empty.

After i change the display language i also change the copy settings for current user and the non-unicode display language options.

following is the code I use to query the result.

public List<string> GetAllCollections()
       {
           try
           {
               List<string> collectionList = new List<string>();
               IResultObject query = SCCMConnection.Current.QueryProcessor.ExecuteQuery("select * from SMS_Collection");
               foreach (IResultObject o in query)
               {
                   collectionList.Add(o["Name"].StringValue);
                   o.Dispose();
               }
               return collectionList;
           }
           catch (SmsException)
           {
               throw;
           }
       }

   public class SCCMConnection
   {
       private static WqlConnectionManager conMgr;
       public static WqlConnectionManager Current
       {
           get
           {
               if (conMgr != null)
                   return conMgr;
               SCCMConnection sccmCon = new SCCMConnection();
               conMgr = sccmCon.Connect(Dns.GetHostName(), null, null);
               return conMgr;
           }
       }
       public WqlConnectionManager Connect(string serverName, string userName, string userPassword)
       {
           try
           {
               SmsNamedValuesDictionary namedValues = new SmsNamedValuesDictionary();
               WqlConnectionManager connection = new WqlConnectionManager(namedValues);

               if (Dns.GetHostName().Equals(serverName, StringComparison.CurrentCultureIgnoreCase))
               {
                   // Connect to local computer.
                   connection.Connect(serverName);
               }
               else
               {
                   // Connect to remote computer.
                   connection.Connect(serverName, userName, userPassword);
               }
               return connection;
           }
           catch (SmsException e)
           {
               return null;
           }
           catch (UnauthorizedAccessException e)
           {
               return null;
           }
       }
   }

Is there anything else i also need to change, after i change the display language?

I test my service under Chinese,Japanese and Italian,it works fine. But it also doesn't work under French. I don't know why.

Please help...