Incorrectly regarded as goof: "Mr. Lebost is introduced as the new English teacher. His charming wife Anita, from Mexico, speaks only Spanish. She then begins to sing "Cielito Lindo" in perfect English, and later "The Doodlin' Song"."
It's not at all unusual for singers to perform in languages they don't speak. They learn the foreign languages phonetically, often singing in multiple languages that are unfamiliar to them.
Anita starts her audition singing while playing guitar but suddenly bursts into a dance backed by a studio jazz band which is nowhere to be seen in Rob and Laura's living room.
Sally and Buddy's show, 'The Gold Rush Girl', is set in the Gold Rush days. Jerry dressed as an Indian chief and Mel as a Buffalo Bill type back this up, but the number that Rob, Laura and Anita perform dressed in penguin-formal black outfits and bowler hats - though cute - is entirely Broadway cabaret and Bob Fosse-esque and nothing to do with any aspect of the old west.
Mr. Lebost is introduced as the new English teacher. His charming wife Anita, from Mexico, speaks only Spanish. She then begins to sing "Cielito Lindo" in perfect English, and later "The Doodlin' Song".