Someone made a python script to automate most of the process. It's much easier and supports custom steam library locations. Check it out here: https://gtm.steamproxy.vip/sharedfiles/filedetails/?id=2909925037
Commands only work if your Steam library is in its default location.

Each step has only one command. Don't try to split them up by line, just copy the whole block.

1. Download the latest release of the patcher (thcrap.zip):
https://github.com/thpatch/thcrap/releases

2. Extract thcrap.zip into your game folder
(This command only works if you downloaded it to the "Downloads" directory)

1. Rename th18.exe to th18_jp.exe

2. Rename thcrap.exe to th18.exe

3. Define the game's location (honestly just paste it in it works)
note: this looks very strange since steam doesn't allow backslashes in guides. still works though.

4. Run the game (not "Game Setting") through Steam

5. Go through the installer and select "English language pack" (the default)

6. On the next page you should see your game. just click next.

7. Click through the next screen and finish the installer

8. Rename th18.exe to thcrap.exe

9. Rename thcrap_loader.exe to th18.exe

10. Add this to your game's Steam launch options

11. Run the game!!!