Hmm, well, that depends on a lot of different circumstances. First and most obvious would be the length of the script. Next, how much work is needed to translate a GUI. Other would be if there are tools readily available or if I need to write some simple tools myself.
Link Here in the link I briefly explained how I do it. I don't really use script tools like Sugoi or GalTransl or whatever, I do it more manually as well as edits. It just feels more accurate to me.The very first visual novel, I think it was Josou Sennen Oukoku, took me probably around a year? I think. Later ones took shorter time. Well, if I work on it every day, before and after work, for hours without doing anything else, than I think around 1 month would usually take me to complete one game of average length.