This guy is stupid, if it was to help the village girl I'd get it, but why go all out to help the country wasting so much of his money no return?
If he wanted to help he could of just bought some books and let them learn things and do it themselves like he did with girl. He isn't even doing what he wants to do (help them) correctly, he is limiting himself to what he teaches them but is still bringing things that should not exist yet into that world.
Heck he could've just sold those fake gems them at half of their local market price and still get rich since he can bring things from that world but not people, I wonder if Japanese are also half assed like in manga in real life.