As I already observed in other posts, any non-English speaking user must talk to a bot in English, since this is currently the only language which is relatively understood by bots.
This is a big obstacle to chatbots widespread acceptance. However, we can require international users to be able to speak English, but we should not assume that everybody is also able to understand specific slangs.
I think that our bots should speak the most generally accepted form of English, as in any international conversation.
BTW, I think that one of the possible practical uses of these technologies is ESL (English as a Second Language). If I use a bot as my English teacher, I assume he speaks a formally correct English.
I don't consider myself as an illiterate, but I hate when someone talks to me using slang or other short forms, often used only in a specific geographic or social area. So I hope that my bot will always speak like a BBC speaker.
