finally
I successfully extract fonts (total 5 files) from K790a (with HK fw) using Customize_upgrade.xml with XS++
use your xml editor, and put in the following

<?xml version="1.0" encoding="UTF-8"?>
<customization>
<file-operations>
<file-op parse-mask="fa" op="copy" source="TPA/PRESET/SYSTEM/FONTS/Sans-Serif_Chinese_Bd.ttf" dest="usb/other/Sans-Serif_Chinese_Bd.ttf"/>
<file-op parse-mask="fa" op="copy" source="TPA/PRESET/SYSTEM/FONTS/Sans-Serif_Chinese_Bi.ttf" dest="usb/other/Sans-Serif_Chinese_Bi.ttf"/>
<file-op parse-mask="fa" op="copy" source="TPA/PRESET/SYSTEM/FONTS/Sans-Serif_Chinese_It.ttf" dest="usb/other/Sans-Serif_Chinese_It.ttf"/>
<file-op parse-mask="fa" op="copy" source="TPA/PRESET/SYSTEM/FONTS/Sans-Serif_Chinese_Reg.ccc" dest="usb/other/Sans-Serif_Chinese_Reg.ccc"/>
<file-op parse-mask="fa" op="copy" source="TPA/PRESET/SYSTEM/FONTS/fonts.xml" dest="usb/other/fonts.xml"/>
</file-operations>
</customization>
and save as Customize_upgrade.xml
now, you need a phone (DB2020 or DB3150 models preferred, but use a2uploader instead of XS++ with DB3150 models) with Chinese fw (can be APAC, Hong Kong, China, Taiwan)
you should be able to get 5 files on "Others" folder if it's successful
now, use your a2uploader, and copy these 5 files (1 xml file, 1 ccc file, 3 ttf files) into
/tpa/preset/system/fonts
turn your phone back on, and you should be able to read Chinese and Japanese on browser, messaging, media player, contacts
it also works with other languages, but you must browse the files at /tpa/preset/system/fonts, and do corresponding change on the .xml file
the next project: add .lng and .t9, I am not sure will the files in K790a work with TM506 (or other DB3150 models), as well as change the Customize.xml