There's a problem in replacing characters that contains (ة) character and (ت) - The SQL Server doesn't differentiate between those two characters! is spite of each character has different ascii code 201, 202 respectively.
DECLARE @strWord AS nvarchar(50)
SET @strWord = 'تفعيلة'
SET @strWord = Replace(@strWord, CHAR(201), 'ه')
Notice that the function 'Replace' did actually replaced both different characters whith different ascii codes!