I want to know the answer to the following question:
What do researchers use back-translation to try to reconstruct when a document survives only in translation?
All the background I'm provided with is that "Portions of the original French-language manuscript were subsequently lost; however, the missing fragments survived in a Polish translation that was made by Edmund Chojecki in 1847 from a complete French copy, now lost.". Is that enough to answer the question?
Answer: no