Before the 20th century, this was basically how every educated non-Chinese person in East Asia would've studied Chinese, since they all would have learned writt

Before the 20th century, this was basically how every educated non-Chinese person in East Asia would've studied Chinese, since they all would have learned written Classical Chinese as part of their education, but would have had to study Mandarin separately. The results were mixed. Ho Chi Minh seems to have done okay. Another Vietnamese compatriot Phan Bội Châu seemed to never really get the hang of Mandarin Chinese despite spending a considerable amount of time in China (although a good amount of that time was in jail).