First I copied as much saved data as possible from an option file that had the right commentary names (it had simply translated the written names to English).
Load it up from Mem Card 2, choose player data, select player names and where the player on your file matches the one on the other, copy. I used evo-web's v1.0 file.
(**When it offers to Copy only to default areas, what does that mean?**)
You can get a lot of internationals like that, their squads don't change much. Clubs, it's more laborious...
I drew out a chart matching the japanese characters on the comentary name screen, checked a few samples under each to hear what each sounded like.
So the first one is Aimar, then Agathe, then Andrade and so on. It's one of mostly the A-followed by vowel type sounds. (there's another that has Alienichev, Albertini, and Anderson's later, A-followed by consonant)
But they do throw in a few odd ones where you wouldn't expect.
The next character down is Carr, Carsley etc...One covers all the Mc's, Mac's etc. Another one, towards the bottom, covers all the Louis-whatevers.
I also went through the first 30 odd screens of the commentary names (out of 321) noting the real player names I could asign straight away, noting which screen they were on.
I don't know which way was working best, but in the end I think it may come down to noting the japanese from a file with the right commentary name, and then searching for that once you have your own file loaded.
Because not all player names are in there, I want to avoid approximate/sound-a-like names, or searching for ones that simply aren't there.