Expression of the week- pardon my french part 2

Hi everyone! How are you today? I hope you are enjoying the new year.
Well, last week I posted a video where you could see a scene of the movie Ferris Bueller's day off.
And on that scene one of the characters used the expression "pardon my french".

Could you guess the meaning of the expression by watching the scene?

If you couldn't guess it I'll explain it to you.

People use this expression before cursing or using bad words to avoid offending the people who are listening to them. It is like saying: "Forgive me for the kind of language I'm using" or "Sorry for my strong language".

Example: Pardon my french, but that guy is a pain in the ass. (really pardon my french! I'm not used to using such vocabulary)

But one question remains. Where did this expression come from? Why pardon my French and not pardon my German or my Spanish?
According to Dictionary.com "One explanation suggests that during the 19th century, the English often used French words in conversation – a foreign language to most people living in England at the time. Realizing the listener may not have understood, the speaker would apologize by saying, “Pardon my French.”
Read more at http://hotword.dictionary.com/pardon-my-french/#HR4Y1wLSvp0dfEyc.99

Now, the French also use an idiom that refers to English: "filer à l'anglaise". Any French teacher would like to explain it??