Why this playing cards are D and B instead of Q and J ?

[emd]

In Danish it would be (B)onde, (D)ame, (K)onge. The Ace is always A, for some reason, even though the name for it starts with an E in Danish.

I'd hazard a guess and say they could be a Swedish set of cards.

Well AMFP takes place in London so I would say not, unless Swedish decks were used for a game that was popular in Victorian London. TCR (and Frictional) like authenticity for the time and dislike out-of-place references (For example, movie posters in a house from the same production company).