If we replace the menu files would this change the font used by the game to the japanese and permit to load all the dlc? Maybe the font is stored on the JPN eboot? Maybe the dlc named are pre-stored also on the eboot? When Niwakun wrote about changing the name of the titles. he might have done that on the eboot and not on the DLC files ?
or Maybe he has a method to decrypt the EDAT to be able to edit them. My opinion is like yours the edat contains files. Each edat is resigned to 3.55 and react decrypt them and resign them.
I asked someone if we are able to have only the decrypted file using react without the resigning and he said it would mean modifying react (and for that we need the source of the apps that we don't have)
I hope we could find some answer soon to be able to at least rename the dlc and use them even in japanese. DLC solution might be found on the EBOOT.