ok, i finished the big thing..
and i wanna make a quick list of the thinkgs i did and the problems i had (and how i solved)
hope is a good idea. ^^

i had a k750c (chinese) CID 36 BROWN and wanted to make it W800c (chinese)

downloaded these files
W800_R1N035_MAIN_CHINA_CA_RED36
W800_R1N035_FS_APAC_1_RED36
W800i_CDA102430_101_R3A_Generic_APAC_1 (custom file)

first step, convert CID BROWN to RED:
i did it following hyperion17 guide:

using "GFlash":
- make sure that your battery is fully charged! (At least 85% up)
- Much better if, before you start Gflash that your phone already turned off and dettached battery.
- Avoid disconnecting the phone while in flashing process!
- FLASHING EROM - BROWN CID36 TO RED CID36 ONLY!
- Start Gflash
- Under the "REPAIR/GDFS/PATCHING" tab,
- enter the RED CID36 RAW erom file (make sure it's RAW)
ex. RED_CID36.Erom (download from topsony or already inside Gflash directory)
- put the battery back in. (do not connect your phone, not yet!)
- then click the "REPAIR/GDFS/PATCH" button
you will get this message:
GFlash version 2.0 beta 6
**** REPAIRING/PATCHING STARTED ****
Turn off the phone.
Hold "C" button and plug USB cable.
- as instructed, hold the "c" button and plug it to the usb cable.
(release "c" button only when flashing process is already starting)
- and just wait till it's done.(in just a minute or so)
- do not shut down Gflash.
- disconnect your phone from the usb cable,
- but DO NOT TURN IT ON!
- remove the battery for a few seconds.
- place it back in. (do not connect the cable, not yet!)
- get ready to flash the firmware... (don't turn on the phone!!)

i did it, and i flashed it with xs++ 3.1 using (downloaded previously):
W800_R1N035_MAIN_CHINA_CA_RED36
W800_R1N035_FS_APAC_1_RED36

following this guide, step 3 and 4: XS++ 3.1 Guide-Flashing, Customizing, Recovering - Top Sony Forums
(REMEMBER TO SELECT "REMOVE SE WAP LINKS"!!!! i didnt do it at first and it was very annoying)
for the step 4, the custom file should match FS, so i used
W800i_CDA102430_101_R3A_Generic_APAC_1

END of flashing ^^

but i also wanted to add italian language, so, i followed this guide to do it
how to add languages to your phone - Top Sony Forums
with a small difference, when finished to do it... i had to MASTER RESET my phone.
before the master reset, italian language didnt appear, after the reset.. it came =)
anyway, BEFORE MASTER RESET YOUR PHONE, REMEMBER U WILL LOSE EVERYTHING U PUT INSIDE, and also will lose many of the original videos, sounds, games....
so save everything u can, before make a master reset...

and about FAR MANAGER... i had a bad error in the begin... while trying to use the SEFP (plugin for sony)
plugin call error
exception occurred
"unknown exception"
........
............
.....
the plugin will be unloaded!
and when push ok...
internal error....
....
....
...
far manager will be terminated

and finally i understood, computer must have a COM port installed.. or the plugin will not load... so, u must make a fake one.. or a real one.. and in my case, i simply turned on the bluetooth.. and it includes a COM port

after this, finally works!!!

last thing i did, was to add hong kong chinese or taiwan chinese.... but no way to add them.... probably the firmware supports only china's chinese.

to do one more attempt
i downloaded FS files from firmware download section and i tried to extract the files using main2raw (or babe2raw, or gextract) & SEFStool4 (i didnt find any other software for this step... i tried with version 4.4 and 4.7 but didnt work..)
but SEFStool4 give me a fatal error coz cant open file version 23....
and i didnt find any way to solve this...

END of language adding... ^^

finally i realized i should remove the wap links while flashing.. coz they are very annoying... and a bit complicated to remove them after flashing

to delete them after flashing (coz u didnt do it before) u should enter in your phone using FAR MANAGER and delete these files:
/tpa/preset/system/custmenu/FM_PICTURES_HOOK_1/FM_PICTURES_HOOK_1.xml
/tpa/preset/system/custmenu/FM_PICTURES_HOOK_3/FM_PICTURES_HOOK_3.xml
/tpa/preset/system/custmenu/FM_SOUNDS_HOOK_1/FM_SOUNDS_HOOK_1.xml
/tpa/preset/system/custmenu/FM_SOUNDS_HOOK_3/FM_SOUNDS_HOOK_3.xml
/tpa/preset/system/custmenu/FM_THEMES_HOOK_3/FM_THEMES_HOOK_3.xml
/tpa/preset/system/custmenu/FM_VIDEOS_HOOK_3/FM_VIDEOS_HOOK_3.xml
/tpa/preset/system/custmenu/GAMES_HOOK_1/GAMES_HOOK_1.xml
/tpa/preset/system/custmenu/GAMES_HOOK_3/GAMES_HOOK_3.xml
/tpa/preset/system/custmenu/cust_menu_data.dat
/tpa/preset/system/custmenu/cust_menu_done_unpacking.dat
/tpa/preset/system/custmenu/SETT_RINGTONE_HOOK_1/SETT_RINGTONE_HOOK_1.xml
/tpa/preset/system/custmenu/SETT_RINGTONE_HOOK_2/SETT_RINGTONE_HOOK_2.xml
/tpa/preset/system/custmenu/SETT_RINGTONE_HOOK_3/SETT_RINGTONE_HOOK_3.xml
/tpa/preset/system/custmenu/SETT_SCREENSAVER_HOOK_1/SETT_SCREENSAVER_HOOK_1.xml
/tpa/preset/system/custmenu/SETT_STARTSHOW_HOOK_1/SETT_STARTSHOW_HOOK_1.xml
/tpa/preset/system/custmenu/SETT_WALLPAPER_HOOK_1/SETT_WALLPAPER_HOOK_1.xml
- and also delete
/tpa/preset/custom/FM_PICTURES_HOOK_1.itm
/tpa/preset/custom/FM_PICTURES_HOOK_3.itm
/tpa/preset/custom/FM_SOUNDS_HOOK_1.itm
/tpa/preset/custom/FM_SOUNDS_HOOK_3.itm
/tpa/preset/custom/FM_THEMES_HOOK_3.itm
/tpa/preset/custom/FM_VIDEOS_HOOK_3.itm
/tpa/preset/custom/GAMES_HOOK_1.itm
/tpa/preset/custom/GAMES_HOOK_3.itm
/tpa/preset/custom/SETT_RINGTONE_HOOK_1.itm
/tpa/preset/custom/SETT_RINGTONE_HOOK_2.itm
/tpa/preset/custom/SETT_RINGTONE_HOOK_3.itm
/tpa/preset/custom/SETT_SCREENSAVER_HOOK_1.itm
/tpa/preset/custom/SETT_STARTSHOW_HOOK_1.itm
/tpa/preset/custom/SETT_WALLPAPER_HOOK_1.itm

ok, that's all i did

hope it can be useful for someone else ^^

thanks to everyone and a special thanks to hyperion17 !!