Korean and Japanese
Korean language, however, is much closer to Japanese. The grammar is very similar, and both have imported about half of their vocabulary from Chinese, which makes these three languages almost mutually understable in the written form, thanks to Chinese characters (rarely used in Korea nowadays, except in place names). Native Korean and Japanese words are often related when comparing Old Korean and Old Japanese, but few of them are really obvious to modern speakers.
Mindset and values in Japan and South Korea are deeply intertwined, thanks to the strong influence of Confucianism, Taoism and Buddhism in both countries. This is obvious from the corporate culture (e.g. discipline, seniority system), the strict politeness system, or the Taoist/Buddhist value of simplicity and humility. These cultural aspects all ultimately stem from China. That's why Japan and Korea are considered branches of the Chinese civilisation.