: Open language.conf with a text editor like Notepad.

Pretty late, I had the same problem, from what it looks like is that the language is called "Unicode" so just go to a file named " DeviantArt·Pein-Sempai PAINT TOOL SAI HELP!!!! by Pein-Sempai on DeviantArt

: Go to the SAI 2 installation folder and open sai2.ini . You may find a setting to toggle between "English" and "Japanese."

: Many users prefer to download a community-translated language.conf (such as the Alternate English UI on DeviantArt) and replace the original file in the root folder. How to Change Language in Paint Tool SAI 2