The custom file should match FS, so you should choose
W800i_CDA102430_101_R3A_Generic_APAC_1
You can find IT.lng and IT.T9 in download section(w800_Language_EUROPE_5).
Here's the tutorial:
http://www.topsony.com/forum/upgrade...html#post24628
And here's the edited customize.xml you must replace the one from your phone with(unzipped):
customize.rar