I think Columbo doesn't speak italian, I remember in Strange bedfellows when Columbo is brought before Fortelli, the mafia guy, he doesn't speak italian although Fortelli tries to speak Italian to him, Columbo doesn't have a clue and just stares.Does he prove to speak italian anywhere else?
This has come up before, and my take on "Strange Bedfellows" is that Columbo pointedly refuses to speak in Italian to the mobster, just to snub the mafioso's attempt to use Italian to buddy-up to him.
We know (and I personally don't think the writer forgot) that Columbo does speak fluent Italian. It seems to me that Peter Falk conveys this in the way he looks Fortelli in the eye while claiming he doesn't speak the language. His expression seems to say, "You of course know that I do speak Italian -- but only with my friends! I am a cop, you are a criminal -- and I do not consider you my paisan. Don't try that 'we are fellow Italians' stuff on me."