We could consider a preview button, as well as a "5 minute window" to go back and edit after you post. I'm hesitant to implement phpBB (though we ARE considering a third-party tool) because it's a common target for hackers/spammers.
I don't know that we'd enable too much in the way of multi-language support because moderating would become several times more difficult for us.
The forum software for AG3 will ... support all of the usual features you'd expect from a bulletin board
Uh, maybe not ALL of the usual features. It depends on what we build or implement.
A "new post while you were posting" ... that's more difficult to do because your browser would have to keep pinging the server asking if there were any updates since you started writing your post. That's not likely to be something we'll implement.