I know absolutely nothing about the Japanese language, and I used this method to help me find the ROM addresses of some Japanese text. This should work on any platform (Genesis/MD, NES, SNES, etc). It should also work on any language.
I'm sure lots of people already know about this method, but it can't hurt to post it...
If the game you're trying to translate has a screen that lets you enter your name or a password, you can use info on that screen to help you find the ROM addresses for some of the Japanese (or whatever language you're looking for) text. Here's an example of a "Enter Your Name" screen...
If your screen has English letters (like the one above), just use an emulator with a built-in RAM search program (like Kega Fusion, etc), put the cursor on the letter "A" and search for a hex value of 41. Then put the cursor on the letter "B" and search for a hex value of 42, etc. You should quickly get your search results down to one match. If there are no English letters, then just keep doing a "Different than previous" search each time you move the cursor.
Once you find the RAM address for the value of the characters/letters that the cursor is on (make sure it's in hex), then you can easily make a short hex string to search for in the ROM with a hex editor. Just find some unknown text in the game (Japanese, Russian, etc), then find the matching character/letter in the password/name screen and the matching hex value from the RAM address you found above. 3 or 4 characters is usually enough for your search.
Keep in mind that not all text in a game can be found using this method.
Like I said before, I'm sure lots of you already know this stuff, but there may be some translation beginners (like me) that this info might help.