Both Don Diego and his daughter Elena are played by Welsh actors, Alejandro is a Mexican played by a Spaniard, and both villains (the probably Spanish Montero and the French Armand) are played by Englishmen.
As a point of interest, this is the first Zorro movie where the hero is played by a real Spaniard as in the books. Unfortunately, this version is Mexican.
Follow the Leader: In a strange double-edged example, The Mask of Zorro may have inspired the film version of The Count of Monte Cristo; but Zorro also seems to be a retelling of the Monte Cristo story (it's actually a retelling of The Curse Of Capistrano).
Throw It In: Anthony Hopkins was very proud of the work he did mastering the bullwhip and insisted they let him show off a bit. The scene in the cave where he's extinguishing candles with the whip? That was Hopkins.
You Look Familiar: Pedro Armendariz Jr. plays both Don Hector and Governor Riley. In addition Tony Amendola plays Don Luis and Father Quintero, the name of the villain in the Tyrone Power film was Don Luis Quintero.