Korea
Hangul Day (also spelled as Hangeul Day) is a day that celebrates the creation of the Hunminjeongeum (Hangul, Korean alphabet), which was inscribed to the UNESCO Memory of the World Register in 1997. Hangul was created by Sejong the Great in 1443 and proclaimed in 1446. Before the creation of Hangul, people in Korea (known as Joseon at the time) primarily wrote using Classical Chinese alongside native phonetic writing systems that predate Hangul by hundreds of years, including idu, hyangchal, gugyeol, and gakpil. However, due to the fundamental differences between the Korean and Chinese languages, and the large number of characters needed to be learned, there was much difficulty in learning how to write using Chinese characters for the lower classes, who often didn't have the privilege of education. To assuage this problem, King Sejong created the unique alphabet known as Hangul to promote literacy among the common people. Hangul Day was founded in 1926 during the Japanese occupation by members of the Korean Language Society, whose goal was to preserve the Korean language during a time of rapid forced Japanization. Today, both South Korea and North Korea celebrate Hangul Day as a national holiday.Sources
Choe Sejin
Choe Sejin is mostly known for his 1527 work, "Hunmong Jahoe" (훈몽자회). It is a textbook for children to learn the Chinese characters, and is known to be very practical in its teachings. During the Joseon Era, literacy in Chinese was an essential skill for advancement in society. Chinese was the dominant language of literature at this time, and children were taught Chinese from an early age to prepare for the future. Although hangul, the Korean orthography, existed by this time, it was not widely used in the country. Choe wanted to promote the usage of hangul through his work "Hunmong Jahoe". As a textbook for children to learn Chinese, "Hunmong Jahoe" incorporated hangul in the textbook to promote both the learning of Chinese characters, as well as hangul. The Chinese characters were annotated in hangul, and in order for one to understand and learn the Chinese characters, one must have a full grasp of hangul first to comprehend the annotations. Choe wanted people to use hangul more extensively, and he thought that this would encourage people to take some time to fully learn hangul, before starting to learn Chinese. He wrote that "it would take [only a single day] to learn Hangul", commenting on the simplicity of hangul, and afterwards, one would be able to learn Chinese on their own without an instructor if one knew hangul and utilized his textbook.