It matters for bcrypt/scrypt. They have a 72 byte limit. Not characters, bytes.

That said, I also think it doesn't matter much. Reasonable length passphrases that could be covered by the old Latin-1 charset can easily fit in that. If you're talking about KJC languages, then each character is actually a whole word, and you're packing a lot of entropy into one character. 72 bytes is already beyond what's needed for security; it's diminishing returns at that point.

If the same user can generate the same input, it will result in the same hash.

Yes, if. I don't know if you can guarantee that. It's all fun and games as long as you're doing English. In other languages, you get characters that can be encoded in more than 1 way. User at home has a localized keyboard with a dedicated key for such a character. User travels across the border and has a different language keyboard and uses a different way to create the character. Euro problems.

https://en.wikipedia.org/wiki/Unicode_equivalence

Byte length of the character is irrelevant as long as you’re not doing something ridiculous like intentionally parsing your input in binary and blithely assuming that every character must be 8 bits in length.

There is always some son-of-a-bitch who doesn’t get the word.

• John F. Kennedy