You could certainly try to do that, though there are a few rules to follow so the .json file containing all the dialogue doesn't break. On the Main Menu, in Translations, then DIY Instructions, there is information there on how to get started and what to look out for.
Viewing post in Amelia's Stranded Adventure comments
Oh, I guess I misunderstood. So, I don't think so. The code for the game has to look up the dialogue using specific values. There is no way to add your own custom value and expect the game to read it. The game would need to be told to look up any new dialogue.
The best you could do is add onto the dialogue currently in the Dialogue-ENG.json file, but I don't think that's what you're asking. Each line of dialogue is contained in a set of quotation marks, so you could try to add more to the dialogue there as long as it is within the quotation marks.