Note--if you need more explicit instructions, click here for a page designed for less tech savvy readers.
Here are step-by-step instructions for converting your English-language Dell Axim X30 PDA to Japanese. I found this info online, tried it myself, and it worked. This is the concise version for people who don't need the hand-holding of the other one.
First, a few caveats.
The Risk: It worked for me, but I'm not knowledgeable enough to be able to guarantee that the conversion will work for you, nor can I be of much help troubleshooting if it doesn't. I'm not an expert--you should use your own judgement in deciding whether or not to attempt this. First off, Dell doesn't want you futzing around with their OS--doing so will void your warranty. If it doesn't work at all, you should be able to back-up to your previous (English) OS, in which case you'll still have a working English PDA, but if you'd bought an English Axim especially to convert to Japanese, you'll be out of luck. While I don't think it's likely (remembering that I'm not an expert), attempting this conversion might completely destroy your Axim, leaving you with a very expensive paperweight. So read these instructions and consider the risks carefully before trying this. Again, I didn't think it was too dangerous to try myself, and many other people have done this, but if you choose to do it you are taking a risk, and if it doesn't work I will not be responsible for your loss. If you decide to try this, you're doing it at your own risk.
The cost: A successful conversion will completely wipe your Dell's memory. Everything on it will be lost. Back everything up by sync before you begin. Also, note that some programs designed for the English version may not work on a Japanized Dell.
The necessary conditions: Finally, the way this works, you can do it only if your Axim's ROM is an older version than the newest English update available on the website (check System\System Information under the settings menu on your Axim to see what version you've got). For example, if your Axim is A05 and the latest update is A06, it'll work. If your machine is A06 already, though, it won't, because the updater will decide you don't need an update since you've already got A06. There MAY be a workaround for this--see the note near the bottom of this page.
1. Download and install XVI32 Hex Editor (get the free version; google it if link goes bad).
2. Download and save to your desktop the latest English and Japanese system updaters from Dell, taking note of which filename is for the English and which for the Japanese (see the Axim support section of the Dell site for other languages or for the latest links if these are no longer valid).
3. Click on each downloaded .exe file to start it. Keep clicking OK until you get to DO YOU WANT TO UPDATE ROM. EXTREMELY IMPORTANT: When you get to DO YOU WANT TO UPDATE ROM choose NO. For DO YOU WANT TO BACKUP/RESTORE A ROM choose YES then choose to SAVE a backup. Make a note of where the program is creating a new folder for the installation files (it'll tell you).
4. Go into the folder created for the Japanese version (those notes about filenames you took in Step 2 and about folder locations in Step 3), open the ROMS folder, open the Japanese folder, and you'll see two files. The only difference in their names is that one has a C in the middle and the other an N. Choose the C if you have the combo (Wi-Fi and Bluetooth) version, N if you have the version without Wi-Fi and Bluetooth. Open the appropriate file with XVI32 Hex Editor. Size the window to fit in half your monitor and put in the bottom half of your screen.
Then do the same for the English version and put it in the top half of your screen.
5. This is where you do surgery on your OS. Select and delete the first 100 characters of the Japanese .IMG file. (To select in XVI32, choose the first character, then select "Block <n> chars..." from the Edit menu, then in the pop-up window enter 100, then click OK.
Now, in the English version, select the first 100 characters and copy them to the clipboard.
Finally, paste the the first 100 characters of the English file at the beginning of the Japanese file, rename the Japanese file to exactly what the English file was named, and replace the English file with the Japanese file. You've now got a Japanese ROM image that will tell the installer it's the correct English ROM image.
6. Run the setup.exe from the English updater, and this time when you get to "DO YOU WANT TO UPDATE ROM" choose "Yes." Make sure your PDA is in its cradle with power and USP cable connected, follow the onscreen directions, and you're all set. Note that there'll be a couple of periods where the thing just sits there for a long time--this is normal. Just don't touch anything and don't use the computer for anything else until it's all done, unless the installer asks you to. This will take quite a while.
Potential workaround if your Axim is already running the same ROM version available on the Dell site. I would definitely not buy a machine with the same ROM version as the newest one online and count on this working--but if you've already got one, you might as well try it. After you've copied the first 100 characters from the English ROM to the Japanese in Step 5, in the right-hand part of the main window you'll see the version number of the ROM (something like "A06"). Change the number to something higher than what's already on your Axim; i.e., if your PDA is A06, then change the version number in the ROM to A07. This seems like it should work, but again I have no idea if it really will. I suspect that even if it doesn't work it'll just shut down the installer without altering your ROM, but I can't promise it won't turn your PDA into an expensive paperweight. I'd be confident enough to try it on my own equipment, but I can't take responsibility for yours. Remember, I'm not an expert, so you're doing this at your own risk.