Complex sentence: In 1949, he became a professor delegate, when his teacher Jean Deny, retires, then, in 1957, full professor at the ENLOV (later National Institute of Oriental Languages and Cultures, INALCO).
Split into simpler sentences: In 1949, he became a professor delegate after his teacher Jean Deny retires. In 1957, he became a full professor at the ENLOV (later National Institute of Oriental Languages and Cultures, INALCO).