Hi @Fabiano! thanks for contacting us about this. You are right, the en.ini file contains the text of the program, so creating an it.ini is the first step for the translation.
Then you can create a package (create a .zip and rename the extension to .aseprite-extension) to distribute your translation, the .zip must contain your it.ini file and other file named package.json: Aseprite - Docs - Extensions
In the languages project you can see some examples about how to package other languages, for example French or Portuguese.
I hope it helps!