I'm willing to concede that, for example, Latin poetry translated into Italian might lose very little in the process, due to the similarity of the languages (or Spanish to Italian and vice versa). I could also see translation from, say, Norwegian to Swedish as being a relatively effortless matter (though why even bother at that point?).

Too much of poetry has to do with meter, sound and emotion for the sense to be easily passed along into another language. After all, you can translate the Chinese "shi" poem (see link), but it's pretty much meaningless to do so.