Sorry. Yes, I did not understand what you specifically need to write a new script
"to ADD language to a game that has only one, in the 'SCEENS.RPY' files I should use? " - ??? "either skis don't go, or I'm a fool"(russian slang), but here it is indicated that you need to add a language - using post #1, No? decide whether you need to add another language or replace - these are two big differences and two completely different methods of translation, why should I think out for you if you cannot formulate your idea?
If you want to write a new script(renpy), the first thing to learn is the syntax of this language, isn't it? And if you need ready-made, then this is only if someone has nothing to do and/or have "free - time of the wagon"(russian slang)