The translation is the real thing because it results in coherent texts wherever it’s tried; multilingual texts are one of the reasons the pronounciations were figured out, since there were cuneiform texts containing already known languages (such as Greek). The archive of Hattusas in Anatolia was filled with tablets which could be pronounced but were not in any known language; Emil Forrer (Swiss, but the name looks French, and of course he spoke German) started to notice words that were German-like, which led him to crack one of the four or more languages found on the various tablets, and reconstruct an extinct IndoEuropean language.
Oh, I believe you that they cracked the general sounds of the language, but how French sounds by even a GOOD American student, by a Parisian, and by a Canadian sounds so different.