Hi! This Desktop version, as well as the Desktop version for the Stan ending, were made in Ren'Py, while the Web version for both endings was made using Monogatari (while Ren'Py does have some Web support, we had issues uploading Ren'Py Web versions due to file size limits here on Itch). The original Swooning Over Stans game was also made in Ren'Py (I'm not affiliated with the creators of the original game, just a fan).
To add a translation to the original game, you'll need to decompile the files in the original game folder first. After you decompile the files, then you can add Portuguese translation support. Here's Ren'Py's official documentation on game translation, and a tutorial on it.
Let me know if you'd like any further help (or if you'd like to translate the new endings too)!