Of these possibilities, the Korean-Japanese connection is most worthy of attention. Given the geographical proximity and the makeup of the peoples living in these countries, it is natural to suppose some kinship between these languages. Moreover, Korean grammar is quite similar to Japanese and its resemblance to the Japanese rhythmic structure in speech is uncanny. Similarities end here, however. In Japanese, a typical rhythmic unit (called mora) has an open consonant-vowel (CV) structure, while in Korean, a canonical syllable is closed having the CVC structure. Vocabulary, too, is another matter. Korean and Japanese both borrowed a large amount of Chinese vocabulary (compare Chinese tushuguan 'library', Korean tosekwen, and Japanese toshokan), thus the fact that Korean and Japanese share a large number of Chinese vocabulary leads us nowhere. But if one compares only indigenous words, one finds that Korean and Japanese share very few common words. The prevailing opinion about the connection between these languages is that, frankly, no one knows. This is due to a lack of conclusive data that can show one way or the other about such a putative relationship. If there is a connection between the two, the time depth of their separation from a common ancestral language may be so remote that much evidence for it has been lost. At this time, any such evidence, if it exists at all, is well beyond detection by the power of current historical linguistics.
Neither Japanese nor Korean seems related genetically to Chinese. Chinese belongs to a group of languages called Sino-Tibetan, a family that includes such languages as Tibetan and Cantonese. Chinese is SVO and Japanese and Korean are both XV. Chinese is a tone language (having distinct meanings differentiated by pitch) though Japanese too is similar in that high and low pitches can sometimes differentiate meanings (e.g., HAshi 'chopsticks' and haSHI 'bridge'; see below on the Japanese sound system). Ryukyuan (or Okinawan), spoken in Okinawa Prefecture, has been found to be related to Japanese. Ryukuan and Japanese are not mutually comprehensible (thus they appear to be different languages), but the comparative method has demonstrated that Ryukyuan retains much older forms of Japanese. Dialects of Japanese spoken in islands between Okinawa's main island and Kyūshū were found to embody characteristics that suggest that grammar and lexical elements gradually moved away from the mainland dialects. For these reasons, if we take mutual intelligibility to be the yardstick for determining dialect status, Ryukyuan must be considered to be a separate language from Japanese, as opposed to a mere dialect, although the historical connection is definitively proven. The similarity between Ryukyuan and Japanese may be likened to that between Italian and Portuguese.
Is Japanese at All Like Chinese?
No and yes. First, Japanese is unlike Chinese since, as we saw above, the grammars of these languages are quite different. Chinese is SVO; Japanese XV. Words are not formed of compounds as much in Chinese (which is a characteristic called "isolating" or "analytic") as they are in Japanese (which is called "agglutinating"). However, consider this: the Japanese did not have their own writing system until the third century, when Japanese scholars decided to appropriate China's writing system.