Jerry Fresia raises a very interesting question. He says "I would imagine too that the various editions of Capital (in languages other than German - and I am assuming this was Marx's essential language for writing) wouldn't carry along the subtlety and nuance from the original German."
Generally speaking, this is always true of translations, but here are some striking counterexamples. At the very beginning of the crucial chapter on "The Buying and Selling of Labour-Power," in which the secret of profit is finally revealed, Marx writes, "müsste unser Geldbesitzer so glücklich sein etc etc." The proper translation of this is: "the possessor of money must be so lucky as to find, within the sphere of circulation, in the market, a commodity, whose use-value possesses the peculiar property of being a source of value etc etc."
The correct translation of Geldbesitzer is possessor of money. But in the English translation done by Marx's son-in-law [among others] and overseen by Engels himself, this passage is translated "Moneybags must be so lucky etc etc." This is, of course, the source of the title of my second book on Capital. Now Moneybags is a simply perfect translation of Geldbesitzer. It conjures up those marvelous nineteenth century caricatures of capitalists as fat little men in top hats and tails with dollar or pound signs on their chests [see the old version of the board game Monopoly.] It exactly renders Marx's mocking tone throughout the opening chapters. And it references the etymological root of Geldbesitzer as someone sitting on something [a bag of gold.]
Here is another example. In the famous Chapter One, in which Marx goes on for pages about the relative and equivalent forms of value [see Chapter Three of Moneybags, "Mrs. Feinschmeck's Blintzes, or Notes on the Crackpot Categories of Bourgeois Political Economy"], he speaks of linen exchanging for coats. He says at one point, as Aveling et al. translated it, "the coat officiates as the form of value." The German verb is gelten als, which means to be regarded as or to be considered as. But throughout the chapter, Marx is playing brilliantly with the idea, which is central to his critique, that in a capitalist society people are treated as things and things as people [this is why he was such a fan of Dickens, who does the same thing in his novels.] Aveling, Moore, and Engels' translation "officiates as" captures this perfectly. One can just see the coat bowing politely to the linen as they go through their minuet of relative and equivalent value.
As for the French edition, which Marx personally oversaw, I have read a good deal of it [to improve my French -- lots of luck], and found that in French Marx sounds like Descartes. But then, I have read In Defense of Anarchism in French, and I too sound like Descartes. It occurred to me that in French, everyone sounds like Descartes.