What language was the Book of Enoch written in?

The Book of Enoch was almost certainly composed in Aramaic, as confirmed by fragments discovered among the Dead Sea Scrolls at Qumran. A substantial portion also survives in Greek, though only in pieces, while the complete text of all 108 chapters exists solely in Ge'ez, also known as Classical Ethiopic (Ethiopian Canon - 1 Enoch in the Ethiopian Canon: The only complete witness).

Every modern English translation draws from these Ethiopic manuscripts, which preserve the full work that would otherwise be known only from quotations and scraps. The Ge'ez version itself was produced around the fourth to sixth century, translated from a Greek intermediary that had earlier been rendered from the original Aramaic (Ethiopian Canon - 1 Enoch in the Ethiopian Canon: How it survived).

This unique survival in Ge'ez, the ancient liturgical language of Ethiopia, means that every complete copy of the Book of Enoch in the world remains in that tongue, safeguarded by the Ethiopian Orthodox tradition (Ethiopian Canon - 1 Enoch in the Ethiopian Canon) (Glossary - Glossary: geez).