in fact i found in this thread
http://forum.xda-developers.com/showthread.php?t=665564 this post
TUTORIAL: DEBRANDING AND UPDATING YOUR XPERIA X2
1º Open SEUS, start a new update. EVEN IF IT SAYS YOU HAVE LATEST VERS, UPDATE IT ANYWAY.
2º ONCE IT REBOOTS, CALIBRATION SCREEN APPEARS. RIGHT AFTER CLICKING ON THE CROSSES, IT WILL APPEAR THE SONY ERICSSON LOGO, AND IT WILL START APPLYING THE CABS. PUSH THE RESET RIGHT after it starts applying (hidden behind the stilus, opening the battery cover).
3º After rebooting, the Sony Logo will appear again asking to retry. Press NO.
4º Now you will need a pack with all the cabs from the language firmware you want to change & update your X2. No matter if they are from the old firmware or the last one.The important part is they must come from the firmware with the language you want to turn your cellphone into. you can find how to extract said cabs here:
(damn forum, it wont let me post a link, in this same forum theres a post explaining how to extract roms, seek for it)
5º Once you have the cabs on your SD Card, you have to install them all, one by one. Once you are done, restart the cellphone.
6º Start SEUS again, run another update, force it if it says you have last version and you will get your X2 updated on your desired language.
now I want to know if it is because we dont know which files in the phone that SEUS checks before updating to a certain language that we need to install all cabs or SEUS checks all cabs before updating to a certain language?