Assuming you never change the game's interface language to Japanese/Chinese, the following files in...
...are completely safe to delete. These will net you 1.5 GB of free disk space.

• OPCH.usm
  
• OPJP.usm
  
• EDCH.usm
  
• EDJP.usm
  
• ED2CH.usm
  
• ED2JP.usm

If you play using Chinese or Japanese for the interface language, then just keep the OP/ED files for the language you're using and delete the other two ones that are not in use. Note that you need the delete the files AFTER you changed the game's language.

If you are playing with the Japanese dub and 100% do not care about the English dub, then you may also delete this folder:


This will net you an extra 600 MB of free space. As long as the game does not try to access the files, it shouldn't crash.

If you are playing with the English dub, then you could delete the Japanese dub files instead to save space by deleting the folders inside the "Sound\" folder that also exists inside of "Sound\en\". With one exception: you must not delete these files inside "Sound\adv_voice\":

• 99_s***_xxx.uasset

Where *** is a 3-digit number going from 001 all the way to 127, and xxx represents the other 3-digit number that these files end with.

Path containing the English dub:
Path containing the Japanese dub:
Delete folders:

• adv_demo
  
• adv_voice
  
• g00, g01, g02, g03
  
• n00, n01, n02, n03, n04, n05, n06, n07
  
• sys_voice