i downloaded, put it in game, i was confused why there was 2 of the same file
Because there are two versions of the game available, pretty obvious from the directory name which one you need.
but changed my whole game to japanese
That's because you have messed up your locale settings. This translation fix also fixes the locale, so "en_US" is English and "ja_JP" is Japanese as it should be, it's not reversed any more.
and also seems like it deleted my save
LOL, no clue what you f*cked up, but there's no way that overwriting a single json file in one directory could delete multiple files in a totally different directory...
when i press start game, then it says something on japanese that i don't understand
If you don't understand Japanese, then do not use Japanese locale, simple as that. Use English and all texts will be in English.