Fake American: The actor (Bruce Boa) who played the American Mr. Hamilton was actually Canadian.
Fake Brit: Yes and no. Connie Booth had lived in Britain for so long that she could be said to be actually British. Also played with in "Gourmet Night," where she sings in a perfect but annoying American accent.
Fake Nationality: Manuel, who's from Barcelona, is played by Andrew Sachs, a German-born British actor.