Dumping a script requires you to make a table file and using it and a hex editor that supports table files. Then once both are loaded, you look through the ROM and find text used in the game (unless it's compressed. In that case, debugging to find the compression routine is required.) and document it. Once that's done, you you can either code your own dumping utility (preferable because you can control what you dump), or use a ready made generic dumper.

I generally build my hiragana/katana tables using Windhex's Table Maker function that let's me easily select my japanese characters. I assume this feature is present in other hex editors as well.

I shall set out to war with a katakana in each hand.

Sometimes it's easier to build a table, based on what game your hacking and what gaming console it's for.

For older tile based systems, in some emulators, you can find a tile viewer and look up the tile number. Then add the character to the particular number to the table file. You do need Japanese text display support in order to add and see the characters in a table file. (I use NJstar or EditPad Lite to edit my table files manually)

There are also table file editors that you can use, like Table Manager or Tabular. Those make it easier to make a table file. I use these to set up the basic set of Japanese characters and then use NJStar to add the rest of the characters manually. After you make your table file, double check to make sure your characters are right.

After you have your table file, you can use WindHex32 as a viewer mostly (to locate text blocks and any other data). You can use WindHex32 to dump the text if you wish. However, I don't use WindHex32 as a dumper.

I use Cartographer as a dumper, so that the output file is compatible with Atlas (script inserter). You have to change the end line, end section, end block, etc characters in the table file to use with Cartographer. Reading the documentation for each program will help you.

This is the basic method that I use and sometimes I have to be inventive and figure out a way to make a table file for any game.

If you're unable to find the hex values for a table using an emulator/tile editor (which is fairly unlikely)...then do the following:

1. Use a relative search program.  You may have to be a bit creative to use it with Japanese text, but it still works.
2. If that fails, do the same, except on a savestate (while the text is being displayed).

2 should "always" succeed (unless the text string is overwritten immediately after processing, which'd be very strange).  From there, you'd have to work backwards (with debuggers / assembly) to see how the text got "transformed" from state 1 to state 2, with compression being the most likely culprit, but there are other common cases too.  If it's not compression, you can see where the string is loaded from and check the input (original) against the output (in RAM) and figure it out that way.

Then write-break on the bitmap.