In French the card names are:

Roi ("king"), Dame ("queen"), and Valet ("jack") and suits of Carreau ("diamond") / Cœur ("heart") / Pique or "Schippen" ("spade") / Trèfle ("trefoil" or "club")

So the letters on the three face cards are R, D, and V for King, Queen, and Jack.

I always though the Jack on the face cards represented a Prince or knight, but I see it means a servant or valet.

Another board called unilang has some interesting discussions of card terms from other countries. I'm unable to post the exact link here because Greg thinks v i e w t o p i c is a naughty word .

Search the web for "playing cards and their names" and select the topic under "unilang.org".