The majority of the game's text is stored in "CommonEvents.json" file in the data folder. However, the text for each event is stored as a single line, and has a bunch of code for how the text is displayed in between the text, so I don't think it would be very useful. I found a plugin that extracts text to .txt files, but it only works on maps and not common events, so it also doesn't achieve much, and you would need to put the text back into the game yourself afterwards. I can look and see if there's some other plugin for this if you'd like, however you also might find what you need by searching "rpg maker mv translator" There are some programs that can auto translate text for you while playing, though I'm not familiar with them myself.