In which Academy Awards were all four acting Oscars won by non-Americans for the first time?

The 37th Academy Awards honored film achievements of 1964. The ceremony was produced by MGM's Joe Pasternak and hosted, for the 14th time, by Bob Hope. The awards show was a star-studded one, including an appearance by Judy Garland, who sang a medley of Cole Porter songs in tribute to the composer, who had died in October 1964.

It was the first year since the inception of the Supporting Actor and Actress categories wherein all four acting Oscars were won by non-American performers; this would be repeated at the 80th Academy Awards.

The Best Actor went to Rex Harrison (English actor) in "My Fair Lady", the Best Supporting Actor went to Peter Ustinov (English actor) in "Topkapi", the Best Actress went to Julie Andrews (English actress) in "Mary Poppins" and the Best Supporting Actress went to Lila Kedrova (Russian-born French actress) in "Zorba the Greek".