Four as “shi” is when the word “four” is pronounced as a kanji(Chinese character), the purely Japanese pronunciation of “four” is actually “yon.” Death is also “shi” because it uses the kanji borrowed from the Chinese language, and consequently sounds close to the original pronunciation.

Korean, also being derived from Chinese, is the same. Four and death sound the same due to their Chinese roots, and is equally taboo as it is in Japanese culture. Again, it is this way only because of how four and death are pronounced as “hanja”(Chinese character). In purely Korean pronunciation four is “net” and death is “jook-eum.”

English by comparison is actually a much sloppier language. There is virtually at least one exception to every grammatic rule(why even make rules?), and English is flooded with words that have multiple different meanings. At least in Chinese, Korean, and Japanese, all the homonyms have a different Chinese character behind it. In English, there is virtually no way of differentiating between different meanings of a word in anyway without the use of explicit definitions.