I couldn't decrypt the DLCs, but if someone manages to do it, we can fix the crashing.
i can help with that.
decrypting the dlcs is not a problem but what i fear is the cause of the crashing is not due to the JIS characters being incompatible with the US game. there are ports of dlcs for other game where foreign characters are just displayed as mojibake so technically it's possible for the dlcs to work even if the characters are foreign.
i do not know much about how the dlcs are processed so it's just a postulation. if help is needed in decrypting i can render my assistance.
when the *B.edats are decrypted, they are FPS4 packed, though albeit different from the game files as they cannot repack properly with mamu's fps4pack. reason for costume jp dlcs not working on us version is because of the spacer size being different in the files with header .4Vx in the *B.edats. items dlcs work fine as they do not depend on *D.edats and there is no spacer required, though they can still be translated.