simply put, you have one of hundreds of designs. there is no common circuit and no compelling reason for anyone to spend the hours to figure out what this particular circuit does or how it works and then create an interface.
this is especially hard due to the lack of information.
google digital scale and find out what someone has done, then get that specific make and model scale and follow their instructions.
what makes this a very difficult project is that it is not for a beginner and it will be a one-off. that means spending hours for the end product of one.
there is tons of information about hacking scales. best thing you can do is read it all, read about the circuits, familiarize yourself with the technology, and attempt to measure things. in the end, you will not be a novice.