Cambridge Dictionary definition:

Excuse or Pardon my French is used when you are pretending to be sorry for using a word that may be considered offensive.

For example, excuse my French, but you’re insane.

John, don’t use this kind of language in front of the kids. “Oops, pardon my French, guys!”

What a bunch of morons! Pardon my French!

Tradução: desculpe o palavreado.