Bombay Ducks

A Welsh Rabbit is not a “rare bit”, it’s a Bombay Duck. And a Bombay Duck is a fish.

Bohemian diamond: rock crystal
Bombay Duck: fish (Harpodon nehereus), fish of the family Harpodontidae, found in estuaries of northern India, where it is widely used as a food fish and, when dried, as a condiment. (Enc Brit)
Bronx cheer: raspberry, boo
capote Anglaise (English overcoat): condom
Carthaginian peace: devastate land and kill everybody
Chinese boxes: nesting boxes
Chinese burn: armtwisting
Chinese copy: an exact imitation or duplicate that includes defects as well as desired qualities (M-W)
Chinese national anthem: explosion
Chinese puzzle: fiendish metal puzzle
Dutch comfort: Thank God it is no worse. (Francis Grose’s Dictionary of the Vulgar Tongue 1811)
Dutch concert: Where every one plays or sings a different tune. (Grose)
Dutch courage: false courage given by alcohol
Dutch oven: casserole dish
Dutch treat: everybody pays for himself and no one is treated
Egyptian PT: sleeping
English bath: apply deodorant (Australia)
fichi d’India: prickly pears
filer a l’Anglaise: leave without saying goodbye
French bath: no bath (Australia)
French beads: faux jewellery
French chalk: steatite
French Leave: leave without permission
French letter: condom
French toast: bread dipped in egg and fried
French window: glass door
German silver: alloy of copper, zinc and nickel
Glasgow kiss: nut on the nose
Greek fire: napalm
Guinea pig: South American rodent
Hamburg Steak: not a steak but a rissole
Hobson’s choice: no choice
Indian gift: one taken back
Indian giver: one who gives and then takes back (But it’s the wrong way round: the Native Americans were “given” Manhattan and many other territories. See “White man speak with forked tongue.”)
Indian summer: fine days in autumn
Irish banjo: shovel
Irish confetti: shower of stones
Irish kiss: slap in the face
Irish pennant: stray bit of thread dangling from home made jersey
Irish stew: bones plus carrots, onions, pearl barley
Job’s comforter (Bible): annoying type who reminds you others are worse off
old Chinese proverb: new, made-up proverb with spurious air of antiquity
Parisian diamonds: fused oxide of tin
poor man’s goose: veal
poor man’s lobster: haddock
prairie oyster: raw egg
Pyrrhic victory: “If this is victory, give me defeat.” M-W: A Pyrrhic victory is so called after the Greek king Pyrrhus, who, after suffering heavy losses in defeating the Romans in 279 B.C., said to those sent to congratulate him, "Another such victory over the Romans and we are undone."
Roman pearls: composed of an alabaster core bathed in various different iridescent substances (isinglass, lustrous oyster scales, mother of pearl powder)
Russian roulette: five blanks, one bullet, six men
Scotch mist: fine rain
Scotch woodcock: Welsh rabbit with anchovies
Shanks’s pony: on foot
Spanish practices/customs: old well-established dodgy dealings
Welsh Rabbit: cheese on toast