So the 2.0 Campaign introduced the concept of a language barrier into the lore--which, by the way, is awesome. But it also comes with its problems.
First of all, the campaign confirmed that the CoV and GI/FD speak different languages, and it is hinted that the WP also have their own language. Whether or not any one world is home to multiple languages is unknown, but its even if there are it's likely that each world has a lingua franca that all characters know.
The trouble arises with the FD/GI/WP alliance against the Sleepers. There had to be some
sort of communication going on there, and it hasn't been retconned out yet.
But much more important is the matter of the Overseers. They've interacted with everybody, and talked with everybody. Are they just insanely multilingual, knowing each plane's lingua franca? Personally, I was thinking about this and I don't like that solution (though it is a valid one--they are, after all, a pseudo-immortal race that has watched over ALL of the planes for who knows how long).
The solution to this problem that I came up with is inspired by the Biblical Pentecost.
All of them were filled with the Holy Spirit and began to speak in other languages, as the Spirit gave them the ability.
Now there were devout Jews from every nation under heaven living in Jerusalem. And at this sound the crowd gathered and was bewildered, because each one heard them speaking in the native language of each. Amazed and astonished, they asked, "Are not all these who are speaking Galileans? And how is it that we hear, each of us, in our own native language?"
(This is followed by a list of diverse places where the assembled people are from, ending with "'in our own languages we hear them speaking about God's deeds of power'") Now regardless of your religion, this concept would translate extremely well into IW: whenever the Overseers speak, the listeners always hear it in their native tongue. Likewise, whenever someone else spoke, the Overseers would hear it in their own language. Not only would it be simpler than having them be Massively Multilingual Overseers (MMOs), but it would be just plain cooler.
Another thing I realized as I was thinking about linguistics was that the language barrier wasn't actually necessary, as realistic as it is. You could handwave everyone speaking the same language by pointing out that after the Calamity there was an Aleta on each world, and that her influence on the rebuilding civilizations would explain why they all spoke the same language. But you went for the language barrier (at least, the CoV/Talich interactions in the campaign would seem to imply as much), and I'm gonna give you props for that. Most people wouldn't even think of it, and it adds a level of immersion to the game.