There is no feasible SEO benefit (unless anyone can prove it?)
There is a pain for sharing non Latin links as the link will end up containing %20%32%36 for non valid URL characters and therefore can not be read by human.
https://stackoverflow.com/questions/1547899/which-characters-make-a-url-invalid
My native language is Russian, I study Japanese, my keyboard does not have Japanese characters, how do I alter link to see japan page?
ISO notation is great in every way, everyone use it and there is really no reason for you not to follow it.
http://apple.com/ru https://www.microsoft.com/ru-ru https://ru.stackoverflow.com/ https://ru.m.wikipedia.org/wiki/Языковая_локализация
I have never ever seen someone to make links localized: https://site.com/русский/latest-article Looks very odd to me
storing locale in localStorage is also not good as you can not send a link to a localized page:
- I send localized link to my foreign colleague on his language
- if particular page does not contain say French translation, it is clear how to get alternatives for other languages, and they are linkable. You will have a problem otherwise.
For most of webserves it is no longer a problem to have ../en-us/... instead of ?locale=en-us They can even transform one into another in background, so there is no need to choose less beautiful option to pass locale as query string (?locale=en)