In Beloved Infidel (1993), Frasier (Kelsey Grammer) cannot understand the caller (JoBeth Williams) who is French. It is later revealed that Frasier speaks French fluently when passing notes to Niles (David Hyde Pierce) in this episode.
When Frasier removes the topless playing cards from Martin's toolbox, the face of the bottom card can be seen, and it's obvious they are just a normal deck.