You can always go back, but as Sharp has not released a full ROM for the Cxx0 you need to make (or download) a NAND backup. This is quite easy but the menu you use to do it has some very scray options and you could turn your zaurus into a brick - just ask Foxie.
Most of the English ROMs remove all the Japanese fonts and the dictionary/translator data too - meaning you will need to do some work to read/write Japanese again - but it can be done. The other option (my favorite) is to add all the things you want from the other ROMs to your own machine without emoving Japanese support. I wrote a script that changes all the menus etc to English but leave all the Japanese support on the ROM creating my own custom ROM.
Stu
