Oh dear.
This error pops up when the game is unable to load mplus-1m-regular.ttf in www/fonts. For example, when I remove that file and try running it, it throws the same error.
But if mplus-1m-regular.ttf hasn't been moved from www/fonts, I'm not sure why the program isn't able to load it.
I know RPG Maker MV games can be picky about filepaths, especially on non-Windows devices, which can cause loading errors. However, I don't see anything specifically wrong with yours. In case it is, I would suggest attempting to run the game from a different filepath, but that is all I have.
I apologize for the inconvenience.