As it stands, it's looking like the best way to locate all the text is to use savestate hacking. Right now, we don't have very much text dumped because we just haven't gotten that far into the game. I've beaten it once, but it was on a real system.
Yeap, that was the trick that I showed Neill Corlett BITD for the Ys IV project before taking it over! He had successfully found the decompression code, correctly converted it from PCE Assembly to "C", but he could NOT find a text block searching through the 65 Meg data track - the project under Akimaru and him had stalled up to that point. After I was introduced to him via Akimaru and began working with them to get the job done, I noticed that with the YAME emulator you could save a state file in some town (Minea let's say), dismount the game CD image or eject the drive if using a real disc, and then with just the 512 KB state file and reloading it, you could talk to all of the townspeople and everything would work to a point, up until you'd exit the town, or cause some "event" to occur, etc. You could very quickly load and play the game on any computer without the Ys IV CD. So yeah, it dawned on me, "
Hey, SOMEWHERE in that small 512 KB state file, there's a compressed text block!!" Instead of going crazy trying to find something in 65 MBs of data, your search range was now reduced to 512 KB!
That was a pretty cool moment for me cause I was inexperienced at the time, was trying to learn as much as possible, and here was the famous Neill Corlett from the "Seiken Densetsu 3" SNES project who was stuck on something that I actually managed to help him with which finally led to the dumping of the whole script! His knowledge, compared to my knowledge at the time, I mean, he was at a genius level... I never even learned to understand the decompression algorithm, but thankfully, I didn't have to (thanks to David Shadoff).
Unlike in your case though, we were lucky because each block (except for the last) begins with the text for the menu system and "PLAYTIME" doesn't get encoded by the compressor. I actually spotted "PLAYTIME" while browsing a state file and pointed Neill to that offset, and next thing I know, the whole script is dumped!!! For whatever reason, Hudson had to repeat all the menu text with each and every area, so as a result, every text block begins with a unique stream of bytes! The only oddball case though was for the DeBug area after you beat the game and get to speak with the Hudson developers, hear their jokes, etc. I had to track that text block down myself (the menu system obviously wasn't needed anymore for that). No biggie obviously!
Anyway, happy hacking/translating!