I think the only thing that hasn't been solved to, at minimum, workable specifications is localization -- as in, taking media in one language and converting it into another. Too much creative work goes into it that -- rewriting jokes that are reliant on cultural references or puns, recontextualizing norms that are unspoken but not universal, even rewriting characters who fit a trope that only exists in a single culture.

Only a general AI would be capable of that, and we may still be decades away from that, since most funding has been diverted away from it towards ML. But for communication? We're already there for the most part. Might not be able to get good machine translation for.... idk, Georgian, but any major language is already good enough to write a business email, so long as the other party knows a machine did it.