If you want to be REALLY clever... since the text prints super slow in these games anyway (only like 1 or 2 characters per frame) -- and since the game effectively comes to a complete halt during that time.... You probably could just read the data off the disk while it's printing, completely bypassing the need to store it in RAM at all. You might have a loading spike of a few frames once the text first starts to print, but after that the printing itself would be fine.
..... assuming the player has the correct disk inserted. If they don't, you have to show the "please insert X disk" prompt and do all that BS.
This is an option, but probably not a very good one. It was a neat idea, though. =)
EDIT 2: This kind of real-time reading off the disk would probably be REAL HARD on the actual disk drive, too, so you probably wouldn't want to do this if this game is going to be played on a real system.
Ha, that sounds like a REALLY bad idea.
In fact, I'd be surprised if it's even possible.
The problem with this request is that you need to understand how the FDS works. The stock NES has just 2KB of RAM, but because it can access 32KB of program ROM and 8KB of character ROM at any time, it's only used for real-time calculations and storing stuff like lives and score and whatever else a game needs to remember temporarily. The FDS, being disk-based (and a particularly slow disk at that), has to load EVERYTHING into RAM, since it doesn't have any ROM (aside from the BIOS, but that doesn't count). So there is 32KB of RAM in the system for the program data, and 8KB for the character data - which makes it essentially the same as a regular Famicom/NES cartridge without any MMC, 32+8KB.
What made the FDS a great idea at the time is that there were no MMCs in use at the time to expand the ROM inside the cartridges, but the disks could store around 64KB per side, for a total of a little under 128KB per disk. Given that the disks were cheaper than cartridges, and could store around 80KB more than regular cartridges, AND could save your game without a battery, AND you could buy new games really cheaply by copying them to a disk using the kiosks in shops in Japan... you could see why it was a great idea. Zelda 1 couldn't have been done on a cartridge at the time.
However, it didn't take so long for MMCs to be used in cartridges to allow extra ROM data to be accessed by the Famicom/NES, and there was no need to load it either. Eventually MMCs had the capability of utilising 256KB of ROM or more, and the use of battery back-up and SRAM in the cartridges increased the possibilities - not to mention extra chips for sound in games like the Japanese version of Castlevania III. Finally, all these games were still perfectly playable on a stock Famicom, so the advantages of FDS evaporated rather quickly, and the system was done.
History lesson over...
So hopefully by now you realise that the FDS uses disks, not ROMs, and the system has a certain amount of RAM, and that's that. If the hackers couldn't get any more text in the game, it's a pity, but there's not much to be done. It's possible that there could be some compression or whatnot, but really I don't think you're missing much just playing it in Japanese. Zelda 2 certainly has more text, but it's still not much. Maybe one day I'll take a look at it and see if I can do a better job, but for now, it's not a priority.