Originally Posted by tiecollector
Japanese and Korean share similar grammar and both are derived from Chinese words. They also share some of the same words. A Korean can go to Japan and become fluent pretty quickly, and vice versa. NR would be a better judge of this but this is what I have heard from Koreans and I associate with many.
Apparently Korean has more words of Chinese origin than native Korean origin, much as English has nearly as many words of French and Latin origin as Anglo-Germanic, but it is still classified as a Germanic language. The question of whether Korean has Altaic roots is very debatable, apparently. It may also be a "language isolate." At least one researcher has suggested an affinity with Dravidian, which seems kind of far-fetched.
Japanese has a good many Chinese loan words, but they are far from a majority of the vocabulary, unlike Korean. The "Japonic" language family includes Japanese and Ryukuan, although the latter may simply be a dialect of Japanese. Any affinities of Japanese with other languages are extremely distant and speculative.
All this is per the Wikipedia articles on these languages, BTW, and nothing I can claim pre-existing knowledge about. Except for dabbling in Hebrew, I have never studied any non-Indo-European languages.