All poetry is poetry in translation.
You have a memory, an experience, a concept, and you translate that into words which approximate to, or can elicit or suggest, an equivalent experience in the mind of a reader.
The actual experience you are writing about will never be directly available to others, but the artful approximation of the experience may be very rewarding for readers.
Faithfulness to the original experience is necessary, but not in itself sufficient for a successful result, whatever we are translating. Someone might capture the essential core of a memory, or idea or experience, and yet the expression or the chemistry of words in the expression might make it uninteresting.
Some translated texts, like Mike's, leave most us with little choice but to trust his faithfulness to the original. But this does not mean (as others have said above)that English-only readers can't talk about the English poem he has made.
Other texts, like those by Homer or Ovid or Horace, are easier to comment upon because there have been so many translations, and so many of them now on line. If you have a solid but rough, literal translation of a passage, and a choice of sometimes dozens of other translations, in both prose or verse, it becomes very easy to "triangulate" (more or less) the meaning of the original. In this way it becomes quite feasible for an English-only reader to have an opinion on whether or not a translation is straying from its source.
Online language resources should not be underestimated. There are many translation sites which can give you a rough literal version like Babel Fish), and other more technically precise sites, like
Perseus, which give you the original text, a literal rendering and an artful rendering. The word-tool also allows you to check on the individual words.
If you click on the Perseus link just above, you will see the first page of Homer's
Odyssey, in a literal rendering. You can also choose to view the same text in the original Greek, or in Samuel Butler's translation. In the Greek view, each word is linked to the online dictionary.
Add to this a few translations from your own shelves, or elsewhere online, and you are certainly qualified to challenge any classical translation for its faithfulness to the original.
There is no reason why anyone here should feel reticent about commenting on translations.