I was reminded about this today and it surprised me yet again:
Japanese is completely unrelated to Chinese, but Japanese use Chinese pictogram based characters to write in Japanese. The pronunciation of Chinese characters in Japanese is often different so while Japanese can read a lot of Chinese, the sounds attributed to the same pictograms in Japanese are different, so Japanese can't 'Speak' Chinese. In fact, a Japanese speaker person reading Chinese pictograms in Japanese will sound like gibberish to Chinese speakers,
Japanese and Korean is closer to Turkish than other Asian languages and some words are similar, but the Korean alphabet is completely different and thus illegible to both Japanese and Chinese.
Meanwhile the origin of the language of the Ainu people in Hokkaido, the northernmost Island of Japan, is a complete mystery.