Hi Lance, an interesting poem. Unfortunately, I think your version needs quite a lot of work.
The first stanza is rough. "Vaunt as evidence" is strained both because it is elliptical (viz. "vaunt as evidence" [of their conquering]) & because it is not in the French, which only says that such a coat "justly belongs" to the conquering monarch. "That's red" in l.2 strikes me as awkward--why not "a crimson coat of arms" or "a blood-red coat of arms"? "Mantled by his mockery" is too vague; because "mockery" is abstract, it makes "mantled" sound metaphorical, or alternatively, one could feel that the coat of arms is a mockery (i.e., the object of mockery) rather than mocking others, when what the French says (I think) is that embroidered on the mantle are mocking men-at-arms (gens d'armes)--presumably mocking first their defeated enemies and second (perhaps) the vainglory of the king. I think you need to phrase this in a more specific, grounded way for it to be clear. "A just thing" at the end of the line has the opposite problem; it sounds too specific, as if the "mockery" is in fact a Just Thing. Without the French I wouldn't know that you intend the general sense of "justly."
I've thought hard about the second quatrain, where we differ pretty widely on the prose meaning of the French. Given the arc of the entire poem, 'pourpre' has to refer to more or less the same color as 'rouge' in Q1; it's a travesty to translate it "purple." Here is my take on the prose meaning of Q2:
O Crimson, fill (/bathe?) my head in your precious fluid (?), and make it [my head, presumably] distill/drip/pour out a thousand crimson tears, so that, while meditating on your mysterious meaning, I bloody these Carmelites with the blood drawn from my eyes.
I have been wondering about those Carmelites; I suppose we are to imagine him in a monastery, meditating over images of the wounded Christ, & wishing that he might weep blood upon the poor attendant friars. In any event, the context is too sanguinary to read 'jus' as law (Latin ius
as you'll know means both law and soup, and gives us not only jurisprudence but also fruit juice and roast beef au jus). I can't find "blood line" or "ancestors" in the French, though that could be my own failure. About your verse I'll only add that line 7 is 6 beats.
You mostly get back on track in the sestet, but the meaning is still a bit deformed in line 9. Presumably the "you" there is still "purple"--your line seems to mean that 'our sin makes purple look bloody,' which doesn't make sense to me; the French meaning is "your bloody color represents our sins." Line 10 is great. Line 11 is good too, although I wonder whether "se charge" in the French means something more like "loads himself" rather than "is charged," i.e., 'charged' in the sense of "the world is charged with the grandeur of God." Also, doesn't "t'endossant" mean "taking you on his back," where "you" refers to the color crimson, but also the weight of the world's sin?
The last half of the sestet is very rhyme-forced. First of all, after all this about color the sins have got to be "red"--that's non-negotiable. I am interested in the "branches of the abyss," mainly because 'des abimes' is plural in the French--I wonder what that signifies? The branches seem to be the red lines criss-crossing Christ's beaten back, but how does the abyss figure in? Hmm, I guess it has to do with where sin leads you, but I don't fully understand. Anyway, "be laid where they are never fit" is an ungainly and inadequate periphrasis for "hide." In the last line, Christ's flesh is being compared to a mantle, in whose bloody folds the poet wants to hide his sins, tying back into the first stanza's imagery. Unfortunately, the appositive in your version does not make that clear, while "we have flayed" is problematic on a couple levels; first, because the poet never explicitly lumps himself in with Christ's torturers, and second, because "flaying" means to cut the skin off, not merely to bloody it with a whip.
Well, interesting poem, that reminds me of Donne's holy sonnets, #4 in particular. I hope these comments are helpful, and that I haven't butchered anything. Best of luck with it,
Edit: I have just realized that the king in Q1 has got to be Christ. Never said I wasn't slow, but I get there eventually...