Yes, I have tested if I load any NTSC-J games with "NTSC-J patch", system will tell me my memory card (which I have NTSC/PAL/NTSC-J game saves) has to be formated.
Not all NTSC-J games need this "NTSC-J" patch unless you would like to have an independent memory card for all your NTSC-J games.
I thought you couldn't have JP and Non JP saves on the same memory card.
Japanese games require the MC to be formated in Shift-Jis.
or does Japanese formated card allow non shift-jis games to be saved too?
I think the complicating factor is the different ways games check the memory card language setting ("format"). If you just skip the region check, many Japanese games will run and save on a card that's flagged for international use, with minor side-effects like
mojibake text when viewing saves in the save manager. In practical terms, the saves work, but they won't work on a real Japanese console because they're the "wrong language". My pure guesswork explanation for this would be that the games check the console's current status (international) against the memcard (international), find a match, and save.
On the other hand, some games have a hardcoded check of the language flag on the memcard, and if they detect a non-Japanese card they'll throw an error and insist on reformatting the card (generally in Japanese, so if the reader can't understand it and just agrees ...). Since these games aren't checking for a match against the console, but specifically for the expected "Japanese" flag, they won't play nice with an international card.
Since you're patching all Japanese games now, when they check console status (Japanese) against the card (international), even games which did cohabitate before--which is probably most of them--will now error and ask to format the card. This means two cards will definitely be necessary, whereas without patching, it's possible (but risky) to play with just one. Also, if you have a Japanese card in, the console's save manager will error and ask to format the card back to international (you can, of course, say no). On the upside, the saves are being correctly formatted and will read and write properly on a real Japanese console instead of the awkward halfbreed saves being created before.
Personally, I prefer the current behaviour, since I have a third-party card with two separate banks selectable by button; I just switch the card to the second bank for my Japanese games, and never have to worry about anything getting formatted. That said, I think it'd be desirable as an option for people who only have one card and are prepared to risk losing all their stuff by playing the "wrong" game. On the whole though, from the save perspective, the current behaviour is much closer to how a real Japanese system behaves.
I'm not sure what the default should be, though. The current one greatly increases the formatting risk, since anyone who runs a Japanese game will format their card if they're not careful/can't read Japanese, whereas before the result was usually just a malformed (but working) save. It's impossible to idiot-proof though, since the risk of running a hardcoded-checking, save-formatting game is always there. I guess you could throw a (disable-able) warning whenever a Japanese GameCube title is launched if you really wanted, but it really depends on how much handholding you want to do.
