So.... Now there is going to be a Dungeon Meshi book in Japan to help learn English

And it's overall a good method. Language learning combos really well with fiction media, there's lots of room to create simple sentences that still make sense within that work (like they're doing with the "recipes"), and the series is popular so it's overall more enjoyable. (A good chunk of language learning is to keep yourself motivated.)

For reference: I've learned the basics of Latin through a similar method, but instead of Dungeon Meshi it was Aulularia (a Roman slapstick comedy). More than a decade later and I still have simple sentences from the method stuck in my head.