Manu,
OK, i take this as good news. Your Zaurus seems to be
healthy and booting, so you don't have a hardware issue
there.
Bad news is that it looks like you're not having a backup
If I factory reset to japanese, will I lose all the software installation and configuration I made so far ?
Sure, after a reset everything is blank, clear, new, reset-ed.
You may try to save some data / applications with a simple
tar on a memory card.
Even for a Zaurus, the old mantra is valid: Backup early, backup often !
Try to save your data, perform a reset and your Zaurus should
be back to work again.
///TRIsoft
Marc Stephan