Here are step-by-step instructions for converting your English-language Dell Axim X50 or X50V PDA to Japanese (Windows Mobile 2003 only). I found this info online, tried it myself, and it worked. I've tried to make this clearer and more explicit than what I found, so it'll be useful to people who might not be so confident about tinkering with their OS. The same method should work for any other language for which an updated ROM is available. This is pretty much the same procedure as for the X30 conversion, which I tried (successfully) earlier.
First, a few caveats.
The Big Caveat: 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 any help troubleshooting if it doesn't--I do not give support or advice for people trying this themselves: there's too much chance of it nor working, I don't want to be responsible, and I don't have time to offer tech advice on something this complicated. If it goes wrong, you're on your own. 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. Secondly, there's a good reason they don't want you futzing around with their OS--screw up even slightly and you've turned your Axim into an expensive paperweight. I don't think it's terribly risky (you'll be backing up your old OS so you can restore your system to that if need be), but I can't say there's no chance at all of things going horribly wrong--I was confident enough to do this to my own Axim, but I'm not confident enough to recommend that anyone else try it. It's up to you to look over these instructions and make your own decision about whether or not you want to try this. If you do decide to do it, I cannot be responsible for the consequences.
The lesser caveats: The conversion will completely wipe your Dell's memory. Everything on it will be lost. Back everything up by sync before you begin. 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 A04 and the latest update is A05, it'll work. If your machine is A05 already, though, it won't, because the updater will decide you've already got A05 and quit. In that case, take a look at this method for how to change the version number in the new ROM to something higher than in the old.
Dell allows you to update an Axim firmware only with a newer Axim firmware in the same language. When the updater starts, it checks to make sure that the new firmware is (1) newer than and (2) the same language as what's already on the Axim. That information is in the first 32 characters of the code from the firmware. So what we do is copy the first 32 characters from the English ROM to the Japanese ROM. Then the installer will think the Japanese ROM is the English ROM and it'll let you install it.
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 (X50, X50V) and Japanese (X50, X50V) system updaters from Dell, taking note of which filename is for the English and which for the Japanese (surf from the Dell USA support site if these links go bad or for other languages).
3. Click on the downloaded English .exe file to start it. The installer will create a folder for the new files on your PC--accept the default and make a note of where this folder is (in mine, it created C:\Dell\Drivers\R106214 for the English). Then a window will pop up in your default browser with a button at the bottom marked "Install." DON'T HIT "INSTALL." Close this window to shut down the installer. Then do Step 3 for the Japanese .exe file.
4. Go into the folder created for the Japanese version, open the ROM folder, open the Japanese folder, and you'll see a file called AximX50v_A01JA.IMG (for later versions and for other languages, the "A01" version number and "JA" language code will be different). Right click on it, choose "Open with" and, if XVI32 Hex Editor is shown choose it, otherwise click "Choose program" and browse to the location of XVI32 and choose it (it's probably on your desktop). Click OK to open with XVI32 Hex Editor. Size the window to fit in the bottom half of your monitor and put it there.
Then do the same for the English version (file is called AximX50v_A05EN.IMG) and put it in the top half of your screen.
5. This is where you do surgery on your OS. In the Japanese (bottom) version, click on the first square in the upper left of the main window to choose it. From the Edit menu, select "Block <n> chars...", then in the pop-up window enter 32, then click OK. You've just selected the first 32 characters of the code; they should turn red. Then delete them (click the "X" button in the toolbar at the top; should be the fourth from the left).
Now, in the English version, click the first square in the upper left in the main window, then from the Edit menu select "Block <n> chars...," and in the pop-up menu enter 32, then click OK. Then, in the toolbar at the top, click the "copy" icon (looks like two pieces of paper; sixth from the left).
Now, click the top blue bar of the window of the Japanese version to go back into that. At the very bottom of the program window, you'll see three boxes, "Adr. Hex:," "char. dec.:," and a third one that says either "overwrite" or "insert"--if it doesn't say "insert," then hit the "insert" key on your keyboard to change it to "insert." Then click on the first square in the top left of the main window and then click the "paste from clipboard" icon (looks like a clipboard; seventh from left). Double check that the first 32 hex codes now the same in both files. Save and quit.
6. Now, copy down the name of the English .IMG file, then delete that file. Change the name of the Japanese .IMG file to the name of the English file you just deleted, and move it into the folder where the English file was.
7. Go back up two folder levels to the folder for the English updater, which should be something like C:\Dell\Drivers\R106214. Click on setup.exe, and this time when you get to "Install" choose "Yes." The next choice you'll be offered is "Backup/Restore" or "Install." Click "Backup/Restore" and then "Create a backup file." This will take a while; when it finishes, it'll quit, so then click setup.exe again, and this time choose "Install." Make sure your PDA is in its cradle with power and USP cable connected, the battery fully charged, and ActiveSync on. Note that there'll be a couple of VERY long periods where the thing just sits there for a long time--this is normal. Unless the installer itself tells you to do something, don't touch your computer or PDA until it's all done. Interrupting the process could be very bad, indeed. Now you'll have to set up your Axim again, just like when it was new. A side effect of the process is that the Axim will freeze for a while during set-up and then run glacially slow. This is normal and by the end of the set-up process it'll be back to normal speed.
You're done. All menus and commands will also be in Japanese now, but if you're not fluent, you can compare what you see onscreen with the screenshots in your English language users' manual (all the menu items will be in the same places) to figure out whatever you need to figure out. Also, your newly Japanese Axim will work just fine with the English sync software on your computer, but it might NOT work with some English Pocket PC software (though it's worked with everything I've tried so far).