Try this program and use it to make a BPS patch: Floating IPS. It can make BPS or IPS patches but IPS patches are not designed to work with files as big as ISOs for CDs, so a BPS patch is what you would use this to create. Just tell it what ISO file is the original and what ISO file is the version you want the patch to change the original into, and it will create a BPS patch file.
There is an alternative, if you think BPS is too slow and don’t care if your patch file is larger. You can try this other program if you want to make an XDelta3 patch: Delta Patcher. Pop in the original Japanese ISO file as the original, the patched English ISO file as the patched version, and then tell it to create an XDelta3 patch. I think that this will be faster than making a BPS patch but the downside is the patch file will probably be much bigger.
So I recommend the first program, Floating IPS, for making a BPS patch, over using Delta Patcher to make an XDelta3 patch. There are other programs you can use to make patches too, but I am not sure about whether they are good or not for making patches for large ISO files. Both of these are quite good programs. As long as you have the original Japanese ISO and the patched English ISO you ought to be able to easily recreate the patch using one of those programs.
Forget what I wrote earlier and have crossed out. I THINK the information I got about BPS being better was probably stuff I read online that was written by byuu, the creator of the BPS format, who tends to be very accurate in his statements although a bit biased in favor of stuff he created himself (which is understandable), but then, I misinterpreted his statements and thought he was saying it was better than XDelta3 when he was actually talking about how it was better than IPS, in terms of creating smaller patch files and being able to process much larger files. Those are true regarding BPS versus IPS, but NOT regarding BPS versus XDelta3, this was my reading comprehension error. I DID correctly get that BPS is quite slow because byuu himself admits this.
Anyway use this program to make an XDelta3 patch: Delta Patcher
(Full version, not Lite version). Pop in the original Japanese ISO file as the original, the patched English ISO file as the patched version, and then tell it to create an XDelta3 patch. It seems this makes smaller patches than the other formats and is also faster, and able to handle very big files. Not just according to me, but according to other people posting in this thread, too, who have actual experience with this sort of thing.