I hate to say "never." but the amount of experience a machine would need to learn in order to emulate human verbal behavior is way beyond what we see now.

Humor is a great example. Sometimes in conversation the opportunity to make a joke arises, maybe to use a pun, or maybe to say "that reminds me of the story about...." To some extent, I suspect endorphins play a role in enabling us to enjoy telling a joke or to enjoy the chuckle it provokes. What machine can summon that motivation? And what machine knows whether a joke (or any particular joke) is contextually appropriate to that conversation? Code switching is about more than diction. Every conversation has its own Overton Window. What we say to our friends and what we say to strangers are very different.

Language is behavior. For a machine to emulate human use of language, it must be able to emulate human behavior that uses languages. Maybe, some day. But one hopes not.