Frequency Module could be used to capture and translate the brain waves of these alien villagers, then you'd be able to trade with them.
That's exactly what I was thinking recently. Maybe craft it with a "translation circuit", found as rare-ish loot in moon dungeons.
Now, what they should trade...
- Oxygen Refill. You give them an empty tank or canister and some emeralds for a full tank/canister. But if we start with that, they could also sell all other kinds of fluids/gases as well, like fuel or nitrogen. Maybe energy, too. On the other hand, not sure how they would be supposed to get their hands on that.
- Meteoric Iron. It's quite a pain in the ass to get it before having access to the asteroid belt, and it would make sense for them to have the stuff.
- Translation circuits/upgraded freq. modules: basically, if you have one, you can get more, for other players or for crafting maybe
- Schematics: not sure about that. There should be more moderately-useful schematics like moon buggys for that, since rockets would be imba
- Seeds and saplings, obviously, since they grow them
- Buying all sorts of stuff from earth: meat, wool, redstone, pretty much anything that exists on earth but not on the moon