In his introduction to C.P. Cavafy's Complete Poems, W.H. Auden admits that if he hadn't read Cavafy's work (in translation from the modern Greek), he would have written many of his own poems differently--Cavafy's work influenced him that much. He goes on to say that this circumstance distresses him because he has "always believed the essential difference between poetry and prose to be that prose can be translated into another tongue but poetry cannot" (vii).
He then performs surgery on his own assumption. He grants that it's impossible to translate homophones and gives this example, by Hilaire Belloc:
When I am dead, I hope it may be said:
'His sins were scarlet, but his books were read.'
That is, the joke, combined with the rhyme, works only in English. The simple example is a place-holder for all sorts of untranslatable elements of language in poetry.
Auden further asserts that when a poet is more of a singer or lyricist than a speaker, the more difficult it becomes to translate his or her work. He cites the work of Campion. I might cite that of Tennyson or Burns--or Hopkins. My goodness, how impossible it must seem for any translator to render Hopkins' idiosyncratic "sprung rhythm" in another language!
Auden goes on to write, however, that we can appreciate technical devices in poems from languages we may not know well or even at all. He asserts, for example, that one can hear the effect of technical devices used in Welsh poetry and that hearing these may influence one's own work.
And he asserts that imagery, similes, and metaphors can usually survive translation, and I think he's absolutely right about that. I'd add only that I think much rhetoric--statements, claims, arguments, opinions--can survive translation, although this is point is chiefly just an amplification, so to speak, of Auden's distinction between "singing" and "speaking."
Auden implies that Cavafy's homosexuality influenced his (Auden's) own work, although, in the introduction, Auden doesn't discuss his own homosexuality. (Although almost everyone who knew Auden seems to have known he was, in our phraseology, "gay," his poetry is certainly "pre-Stonewall" and in effect closeted.) He praises Cavafy's ability to bear witness with regard to sexuality, noting that Cavafy "neither bowdlerizes nor glamourizes nor giggles" when he writes about sex (ix).
Although Cavafy's poetry must undoubtedly be aurally pleasing in its native modern Greek, Cavafy is, in Auden's terms, more of a "speaker" than a "singer," and he is often plain-spoken, as in the beginning of the poem, "On Painting":
I attend to my work and I love it.
But today the languor of composition disheartens me.
The day has affected me. Its face
is deepening dark.
Such a direct voice runs through most of the poems and is, I think, part of Cavafy's appeal, regardless of what the poems concern--and they often concern the past, are set in ancient Egypt or Greece, for example, and imagine the lives of historical figures. Cavafy also has a great sense of irony, and of self irony. Auden observes, "Cavafy is intrigued by the comic possibilities created by the indirect relation of poets to the world" (xi).
In his introduction, Auden wishes he had learned to read modern Greek, and I feel the same way after I read Cavafy, but nonetheless, having the poems in translation is a great gift. I regard the translated poems of Neruda, Lorca, and Machado similarly, even though I know some Spanish. Much of Neruda's "music" may be lost when his poems go into English, but his exuberance, his liberating, earthy surrealism, and his undomesticated imagination cross the divide of translation easily.
The edition of the complete poems by Cavafy (1863-1933) I'm reading is a paperback from Harcourt Brace in 1961. I highly recommend it. It's one of those collections I circle back to regularly, it seems.