I think of something like a comment or an abstract; security is not an issue here because input validation and escaping is done elsewhere.
Basically, I think of a string like "ham, egg." which should result in "ham" and "egg", and "Ветчина, яйцо." should also result in "Ветчина" and "яйцо".
The challenge is that you cannot whitelist all possible characters as there are (imho) too many charsets.