Tile data is stored in chunks... so you'll not decompress all tiledata with 1 unique command... you need to search all compressed chunks offsets. 
Oh, so I am doing it right... it's just not complete.
At least, I found one chunk, so I'll have to find more in the ROM until I have the full font decompressed.
Time to resume spelunking in the FDS ROM.

December 03, 2021, 03:44:47 pm - (Auto Merged - Double Posts are not allowed before 7 days.)
I did some more spelunking in the FDS ROM and found more chunks of data that shows the font uncompressed. I haven’t found all chunks yet, but I’m still holding out hope.
Also on a freak, I tried looking for the ROM’s script in Windhex. It’s uncompressed? The graphics are compress, but the script isn’t?! WTF Konami?!
Speaking of the script, I now need to figure out the ROM’s pointer system. I don’t know if pointer systems on FDS ROMs differ compared to those in NES ROMs. I may have to read up on that later.
Point being, progress is being made. Slow progress… but it’s better than hitting a wall, lol.
P.S.: Typing this on an iPhone with fat fingers is annoying. 🤬
December 03, 2021, 09:23:49 pm - (Auto Merged - Double Posts are not allowed before 7 days.)

And after spelunking further, I FOUND THE WHOLE FONT!!! After poking through myriad offsets, I found the font in one place! (0xE81) Now, the step is to apply an English font and re-insert this into the ROM.
Let's see if I'm successful here. *Crosses fingers*
Anime_world, thank you so much for the tool you recommended! This wouldn't have been possible without your assistance!
December 03, 2021, 10:57:16 pm - (Auto Merged - Double Posts are not allowed before 7 days.)
Back to the roadblock... I after I decompressed the font, I added the English font from Castlevania III to the decompressed file and tried inserting it EXACTLY where I had extracted it in the first place (0xE71). However, when I ran the edited ROM, FCE Ultra (I use that and Mesen for beta testing) gave me a "Disc Trouble Err. 25" message.
What could I be doing wrong here? o_O???
December 04, 2021, 08:18:34 pm - (Auto Merged - Double Posts are not allowed before 7 days.)




I think I made a breakthrough, but I'm not finished yet. After more tinkering, I managed to adjust the offset by two (Inserting at 0xE81 instead of 0xE83. The font could also be decompressed and extracted at 0xE83) and I managed to insert the English font into the ROM and it's running. The problem is some of the sprites were changed as well... not how I had hoped it would work. The last 16 sprites show numbers and letters instead of actual game sprites. I'll have to fix that somehow.
At least, I managed to insert the English font, so that mission seems to be accomplished. I just need to re-add the original sprites that were, somehow, changed inadvertantly.