Eli5 How are dead languages translated to something understandable when found out in the beggining

Question

Eli5 How are dead languages translated to something understandable when found out in the beggining

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Answer 1

By finding it also written in non dead languages.

The Rosetta Stone is a famous example. It was a decree written in multiple languages. I think 2 of them were still known and so it was used to decipher the ancient Egyptian. It though was still a lot of painstaking work as languages don’t normally translate one for one, with the same grammar, etc.