I'm currently in the process of reading Cyrano de Bergerac (translated by Charles Renauld). There, an introduction is made by Adolphe Cohn, said to be the Professor of the Romance languages and Literatures in Columbia University. You can find a copy on Project Gutenberg, here.
… for it is in the nature of great literary works that they consist of a combination of what is purely human with what belongs to the time and place where they have their birth.
Of the faithfulness of his rendering those acquainted with the French language will easily judge, as they can have under the same cover the English of the translator and the French of the dramatist, and they will thus, it is hoped, acquire a clear and adequate conception of the beautiful picture, which, thanks to Edmond Rostand, has restored the life and brilliancy to the somewhat faded features of that eccentric philosopher, poet, hero and gentlemen, Savinien Hercule de Cyrano Bergerac.
Now, he says here that, in order to have a good translation, the translator must be proficient in both the source and target languages, along with an understanding and familiarity of the setting, etc. of the source play.
However, these are some general translation tips, and while I think it does help to ensure a more correct play, I wonder what has been lost in, for example, the translation from English to French. I know that in some cases (e.g. the Bible), certain mappings of words are not perfect; the specific Biblical case would be four different Greek words mapping to "love".
Some other works that come to mind would be Dante's La Commedia Divina (Divine Comedy; Italian to English), many early philosophical works (e.g. those of Plato and Aristotle), and generally any early work of literature.
So, the question remains: What are the challenges in translating a work to, say, English?