To what extent -if any- should a poem which has been translated (or transliterated), say from Hebrew into English, or from English into Spanish be described as a valid piece in it's own right?

Or is that piece thus written, limited to being merely a poor/good "imitation" of the original?

Interesting question UOC. I think the important thing to make sure is that a translation is 'clearly marked' as being a translation in order for the reader to, as it were, forgive any perceived shortcomings in the new words.
I read a lot of Haruki Murakami books and one has to understand that there are glaring 'un-right' expressions from time to time in the texts.

Short story long!! Yes they are poor imitations but we wouldn't get the chance to read them otherwise would we?

Thanks for that Graham.
I don't know where I first heard it, but I seem to remember someone saying that "Language is about ideas": given the ease of today's communication by internet, the world of literature and language etc has become a hell of a complicated one in that respect.

I may have found a partial answer to my original question.
My Penguin Book of French Verse tells me it has
"plain prose translations of each poem".

From what I can see, the translations are not in "verse", (but are they poetry?) and they do not conform to the line breaks of the original.

The British poet T. S. Eliot noted, "the distinction between verse and prose is clear, the distinction between poetry and prose is obscure." https://en.wikipedia.org/wiki/Prose