Thanks for trying the demo and for your interest!
The DLsite version has already been updated to support English, Japanese, and Simplified Chinese—just like the itch.io version.
Although the product page doesn't reflect it yet (they’re enjoying a long weekend in Japan), the actual download files are already the updated ones.
So you're good to go if you decide to purchase it now.
I really appreciate your support, and I hope you enjoy the full game!