Emperor Hirohito’s surrender speech, delivered on August 15, 1945, over the radio, was in classical Japanese that was heavily influenced by classical Chinese, especially in vocabulary and syntax.
Before broadcast, the text was reviewed by two specialists in classical Chinese who not only checked for proper cadence and grammar but also suggested apt classical phrases. (See footnote 2 at p 568, Embracing Defeat: Japan in the Aftermath of World War II by John Dower, published in 1999.)
The speech was not comprehensible to ordinary Japanese. (P 34 Embracing Defeat).
A book that explains well the transmission and learning of Chinese civilization and culture by Japan is “China and Japan Facing History” by Ezra F. Vogel, published in 2019.
Ezra explains that the greatest transmission was from 600 to 838 AD.
During this period, the Japanese learned the art of governing with a bureaucracy, Confucianism, Buddhism, and the Chinese written language; built temples; played Chinese musical instruments; made ceramics; etc.
The Heian period in Kyoto (794-1185) is famous for its high absorption of Chinese culture.