Can translator++ convert a CSV file into a RPG maker MV json file?
I don't think Translator++ can do that, but I'm not sure I even understand your question.
How did you even make a csv that has the necessary information to generate a RPGM MV json file?
Or do you mean you have a csv file with "Original Japanese, English Translation" columns and you want to insert them into an existing RPGM MV json? (If so how did you actually make that csv? Usually programs that do that also have some way of patching it back in, making that less complicated. Otherwise you could try to import the translations in line by line mode.)
Or do you mean you want Translator++ to properly parse the translateable text of a csv file so you can comfortably batch-translate it?
(That's actually fairly easy using the custom Parser addon, you just need a regex pattern for it.)
Or do you mean converting the information of a csv file into a generic json file (array)?
(But why would you need Translator++ for that?)