We're looking at rhythm here, so all you need to know is that Spanish is phonetic, and the vowels are like their short versions in English except for "o," which sounds like it does in "home" and "u," which is more or less like the "ew" in "stew." Don't take this as a lifelong guide to Spanish pronunciation or anything, but it should enable anybody to catch the music in these, the first eight lines of the first poem in the book:
Resbalo de tu cadera parda
amo los otorongos que respiran
lamo tus flancos de marea
arde una cuesta
donde tus pechos
revientan de mangle
de látex de mercurio
polen tibio en su abismo
And in del Pozo and Rattner's English:
I slip from your earthen hips
love the otorongos that breathe
savor your tidal flanks
a slope aflame
where your breasts
burst with mangroves
with latex with mercury
warm pollen in its abyss
As can clearly be seen, the English lines are visually almost identical to the Spanish, and even a slow sounding out will show how closely the English follows the beat of the Spanish. What it takes is a command of both languages to see how Del Pozo and Rattner get this done.
In the first line, where the Spanish gets a lot of its momentum from the letters "d" "a" and "r", they've found a way to keep that momentum, resolving two tricky problems in two different ways. Problem one is that the most basic, literal translation of the verb resbalar is slip and cadera is simply hip. Of course, this gives the English a rhyme the Spanish does not have. This is the kind of spot where a translator might feel compelled to find another, less automatic translation for resbalar, but here they let it stand, to good effect made even better by the solution to the second problem.
Parda is an adjective, the most literal translation of it is brown. Having just made the choice of most direct equivalence, they might easily have done so here, which would have given us the line "I slip from your brown hip." This means what the Spanish means, but it sounds wrong, it's awkward in a way the Spanish line isn't. In short, it doesn't work. So del Pozo and Rattner solve the second problem differently from the first, moving away from literality and towards English poetry by choosing earthen, which conveys every idea of color the Spanish word conveys, but vastly improves the English line, which becomes "I slip from your earthen hip." This second, final version of the line is so much better. It more closely mirrors all the plastic effects of the Spanish version, at the level of language. It's also damn sexy, as is the Spanish. I want an earthen hip to slip from! And having done so, I want to go whereever it is this poem is taking me.
Anyone who might be inclined to think I'm making too big a deal out of this should remind themselves: this is the first line of the first poem in the book. It must be nailed, it must draw the reader in, it must propel that reader deeper into the poem. And it does. But only because del Pozo and Rattner have not gotten hung up on any kind of programmatic approach to the task, resolving two problems in nearly opposed ways, because to do so has given them the results they need.
In the second line they let the noun otorongo stand untranslated. It's an animal, specifically a jaguar, and jaguar would fit in the English line. But otorongo is better here, I think, because the word is a transliteration into Spanish of one of the names for jaguar in Quechua, the major native language in Peru. By letting it stand in their English, the translators have not only preserved some of the essential Peruvianness of this book, but also echoed the effect that word would have on a Spanish-speaker not from Peru, and therefore unlikely to be familiar with Quechua. A lot of theorizing gets done about foreignization/domestication in literary translation, and here I think we see the question handled very well by simply leaving the word alone.
Further down, in the third and fourth lines, we find the opposite happening. The Spanish in line three has a verb, lamer, which literally means to lick. A bit too literal, no? Del Pozo and Rattner go with savor, which is much better, much sexier, and works well with the rest of the lines in their now-lengthening translation. Line four reads arde una cuesta, which would most literally, or "faithfully" if you prefer, be a hill burns which would not work at all. Read the excerpt with a hill burns inserted. Doesn't do it. Now try something a touch better, such as a burning hill. Not bad, but not great. So the translators again get loose with the old fidelity, always fun, and the line winds up a slope aflame, which nails it. It conveys the visual metaphors being made in the poem. It works with the lines above and below it in a way that is truly poetic.
I grabbed the very beginning of the book here, but any random sample will show pretty much the same thing: a pair of good translators being flexible in their approach to the numerous problems they encounter. They make decisions, even within single lines, that would seem to be based on conflicting criteria, but which in fact are not in conflict in any way, because in translation, as in little else, the ends can and often do justify the means.