This film was released on 1987, and was shot by Hollywood directors at great expense. At that time, director China could not spend that much money, and these foreign directors were experts in China, so they respected history objectively. So it is normal to cooperate with them. The reason why English is used is to cater to American tastes. Just imagine, if it is the China version, the doors will not be closed when it is shown in China (people were poor at that time), and the audience may not buy it when it is shown in the United States, so the ticket will be nowhere to be found.