lambdacism: The substitution of an L sound for another sound, or of another sound for L -- especially the R sound. Lambdacisms have often been used intentionally in off-color jokes involving people from eastern Asia.
We've probably all heard Engrish and flied lice, and who can forget the restaurant scene in A Christmas Story where the employees gather together and sing, "Deck the harrs with berrs of horry, fa ra ra ra raah, ra rah rah rah." Those are lambdacisms.
And, of course, there's Mr. Yunioshi, played by Mickey Rooney in Breakfast at Tiffany's.