Question: China said that the Vietnamese culture is the same as China, so why has the Chinese national hairstyle of Manchu never been applied to Vietnam?
Answer: Well, the Manchurian hairstyle or Manchur Queue of China has never been part of the Vietnamese culture. So, the Vietnamese men have never used it as the Vietnamese national hairstyle as China. As all you know, Manchu Queue had been the Chinese national hairstyle for all of the Chinese men and an important part of the Chinese culture within 300 years under the Manchurian rules when Manchuria (Later the Jin Kingdom) invaded China (Ming Empire) and established the Great Qing Empire.
Back to your question, I think that the Vietnamese culture and the Chinese culture share a lot of common things or similarities but also many differences which formed different national identities between the two nations. However, many of the Chinese have only looked at the similarities between the Chinese and the Vietnamese but not the differences which led to the wrong conception of China about the Vietnamese culture, the Vietnamese and Vietnam. One of the differences between China and Vietnam is your question about the Chinese national hairstyle during the Chinese Qing Empire 1633–1911 which has been called Manchu Queue but has never been used in Vietnam at any point in Vietnamese history. I think that there are some reasons as follows:
Firstly , Manchuria or the Later Jin Kingdom (predecessorof the Great Qing Empire led by the Manchurian rulers) defeated China of the Ming Empire and annexed successfully it but it was defeated in Vietnam in 1788–1789 after the Ngoc Hoi-Dong Da battle . There are more than 200.000 Qing soldiers who have been killed and captured by the Vietnamese and the Great Qing Empire could not have any chance to impose its culture of hairstyle on Vietnam.
(Quang Trung - the Vietnamese emperor and also one of the greatest national hero of Vietnam who commanded his troops to liberate North Vietnam from the short-time Chinese Qing occupation and defeated all of the Chinese Qing force there 1788–1789
Anyway, the Manchurian hairstyle has been imposed forcedly on all of the Chinese men which is similar to North Korea today where the North Korean people have certain hairstyle to choose from.
(Kim Jong Uns hairstyle)
Secondly , At that time, under the Vietnamese Confucian framework, most of the Vietnamese saw the Chinese national hairstyle above for men as barbaric culture or uncivilized style. Therefore, the Vietnamese men have never cut their hair like so
(the last Vietnamese Emperor and Empress)
Of course, I do not know whether the Chinese Confucian has a different view from the Vietnamese Confucian or not. So, I wish to hear more share from the Chinese people.