Pepper's comment about Latin

Well, I don't remember the scene exactly, but I'm pretty sure, that this was meant rather sarcastic.

Latin is really not an easy language and has a rather complex grammar. Besides that it's not really spoken in everyday life anymore and only read from ancient texts or used in quite specialized contexts (law and medical terms, recitated prayers), but not spoken in direct dialogue. That's why it's commonly referred to as a "dead language".

So what she probably means is, that somebody who claims to speak Latin (fluently) is either an impostor or some weird genius (or works in Vatican, which doesn't make it any better ;)).

Latin certainly is still spoken, just not widely. From a BBC article, "Now retired to Milwaukee, Wisconsin, Foster continues to speak to friends in the Vatican on the phone in Latin". Foster (that is Father Reginald Foster) is also quoted as saying:

Latin is a language, it didn't come down in a golden box from Heaven. You don't have to be clever to speak it. In ancient Rome it was spoken by poor people, prostitutes and bums.

He also runs a two-month immersion course in Latin, in which "Two nights a week are dedicated to conversational Latin". However, he estimates the number of fluent speakers is very small, perhaps only around 100.

Carpe Diem, Quid Pro Quo, Pro Se, In Vino Veritas, Semper Fi (short for Semper Fidelis)... It's certainly spoken frequently enough as certain phrases have found their way into (almost) everyday life. However, it's definitely not widely used anymore in full.