Query optimization

Hello,I want to optimise the following query that is running so slowly. Please help or gimme an advice.MERGE dbo.LocalizedCategories AS T USING ( SELECT L.LanguageID,SC.CategoryID,BC.Value FROM (SELECT DISTINCT BetradarCategoryID,Value,[Language] FROM #LocalizedCategories WHERE [Language]<>'BET') AS BC CROSS APPLY(SELECT TOP 1 CategoryID FROM dbo.SourceCategories Where Identifier=CONVERT(NVARCHAR(10),BC.BetradarCategoryID) AND SourceID=@SourceID) SC CROSS APPLY(SELECT TOP 1 LanguageID FROM dbo.Languages WHERE LanguageCulture=BC.[Language] )L) AS S (LanguageID,CategoryID,Value) ON (T.CategoryID = S.CategoryID AND T.LanguageID=S.LanguageID) WHEN MATCHED AND T.Name<>S.Value THEN UPDATE SET T.Name=S.Value WHEN NOT MATCHED BY TARGET THEN INSERT ( CategoryID ,LanguageID, Name )VALUES ( S.CategoryID,S.LanguageID,S.Value);