Understanding ECU hex changes for language change

Is there a way to understand the ECU files hex changes applied by the software? I’m new to ECU files and struggling to understand possible areas of interest in the file.

For example, when the language change operation was performed on Prius (through software), following changes were observed:

Now I’m interested in understanding this change. i.e,

1. How could software know this specific offset is the place to make change?
2. How did software calculate new values to replace the old ones?

After some research since a week, what I already came to know is that there are maps defined in files. But I couldn’t find any well documented structure of the files explained anywhere. This is where i’m stuck for long.

Can someone please explain, how can I identify this language change potential area, so that I can try it myself in other car? I have to do it on other car as well, so I’m interested in doing myself. I’m already a programmer, but new to ECU and mechanical stuff. Any help / guideline will be appreciated.