The USA physical version didn't include Japanese voices on the cart, but if you're using NoNpDrm, ensure you grab the "Voice DLC" packs if you want to switch audio languages.
NoNpDrm (This format works by using a "fake" license to run encrypted retail game files on a jailbroken Vita). World of Final Fantasy PS VITA (USA) (NoNpDrm)
The Vita version can struggle with frame rates in busy areas. Many users recommend using a plugin like PSVshell or LOLIcon to overclock your Vita to 500Mhz for a much smoother experience. The USA physical version didn't include Japanese voices
You must have the nonpdrm.skprx plugin installed under ur0:tai/ and properly configured in your config.txt . Installation Guide but if you're using NoNpDrm