Patching instructions

Use UMDGen for this (File - Open Disk Image), 7zip or whatever and extract YUMFILE_*.bin from the \PSP_GAME\USRDIR\ folder into the imas_sp_tl folder. 

YUMFILE_1.bin = Perfect Sun (PS)

YUMFILE_2.bin = Wandering Star (WS)

YUMFILE_3.bin = Missing Moon (MM)

Please make sure to follow its initial instructions. Wait until it finishes, this step will need some time. 

This process will decode all the japanese scripts from the game and re-encode them with the english script lines. When it finishes successfully, it will leave a new, modified YUMFILE_*.bin back at \imas_sp_tl\. If some random gibberish shows up on the command window, patch may have failed (feel free to reach me for troubleshooting).

Open your .iso file with UMDGen (File - Open Disk Image) and place the new YUMFILE_*.bin inside the \PSP_GAME\USRDIR\ folder (Right click - Add - Existing Files or just drag and drop).

Delete all content from the \SYSDIR\ folder and add the EBOOT.BIN located at \imas_sp_tl\.

Press File - Save as - .iso and save it with another name. DO NOT OVERWRITE YOUR ORIGINAL .iso.

Run the imas-patcher-plus.exe located inside \imas-patcher-plus\ and press Select ISO...). After this, press Apply (2-3 warnings may pop but it should be ok).

I would advise you to test your .iso on PPSSPP to check possible crashes or broken texts. You can preview the latter by leaving the game on the "Press Start" screen, since random ingame dialogue will show up after a while. If the text looks ok, everything should be fine.

If something fails during this process, or you just want to check more documentation, more readme files which may provide more in-depth explanations are available inside the /imas-psp/ folder.

Add the files in mail_dlc into your \PSP\GAME\NPXP00100\MAIL\ folder.