When were hieroglyphics decrypted?

Answer 1

When they found the Rosetta stone.
There were many attempts to put meanings to the hieroglyphic signs. The Classical Greek and Roman writers, some of whom had visited Egypt, were unable to read the signs and they believed they did not represent a proper writing system but a kind of code: a crocodile stood for anything evil, a hawk for anything quick and so on.

This idea of hieroglyphs as a code was "confirmed" by the writings of an Egyptian, Horappollo, in the 4th or 5th century AD. He wrote a manuscript that was widely copied for hundreds of years and even published as a book in 1505, giving completely fictitious meanings to each of the hieroglyphic signs.

A Jesuit priest, Athanasius Kircher, pretended to be able to translate the writing, but his readings were also total fantasy. it was only towards 1800 that some scholars began to think that hieroglyphs might include phonetic signs.

In 1814 the English linguist Thomas Young began to study the text of the Rosetta Stone and his findings were a major contribution towards the decipherment, but he was still influenced by the false writings of Kircher and others. It was left to the Frenchman Jean-Francois Champollion to complete the work - the full decipherment was made in 1823.