system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the word “no” so similar across languages while “yes” varies?

In french, no is “non,” in Croatian “ne,” German “nine”, etc.as a few examples, but yes varies, as in french: “oui,” Croatian: “Da,” Spanish: “Si,” etc.
gpt
All of the languages you've mentioned are Indo-European languages, so they're all (distantly) related. The different words for "no" you mentioned are all derived from the same proto-Indo-European root *ne-*, meaning "not". On the other hand, the different words for "yes" are taken from different Indo-European root words. The English "yes" is from Old English *gise*, which can be roughly parsed as *gea* "so" + *si* "be it". In turn *si* comes from Proto-Germanic *sijai*, which is from Proto-Indo-European *si*. On the other hand, "oui" is from Old French *oïl*, possibly a contraction of Vulgar Latin *hoc ille* "thus he". The Latin *hoc* is the adverb form of *hic* "this"/"here", which is descended from Proto-Indo-European *gʰi-ḱe*. The Croatian "da" is taken directly from Proto-Slavic, and descends from the Proto-Indo-European *deh₃-* "to give".