HI: How to set the default font for different language in the xubuntu?

For example, I am using xubuntu9.10(English release),and I do not like the default English and Chinese font.

I have tried to use "Application-setting-appearance-fonts" to edit the default font,however it just work for the English.

The default font of Chinese is "WenQuanYi Zen Hei". I do not like it. I want to use "Microsoft YaHei", I copy this file from my Win7 system.

And I tried remove the "WenQuanYi Zen Hei" by "sudo aptitude remove ttf-wqy",it show me it is successfully removed.

Also I have modify the file:

/etc/fonts/conf.avail/69-language-selector-zh-cn.conf 

to:

<fontconfig>

 <match target="pattern">
  <test qual="any" name="family">
   <string>serif</string>
  </test>
  <edit name="family" mode="prepend" binding="strong">
   <string>Microsoft YaHei</string>
   <string>AR PL UMing CN</string>
   <string>AR PL ShanHeiSun Uni</string>
   <string>Bitstream Vera Serif</string>
   <string>DejaVu Serif</string>
   <string>AR PL UKai CN</string>
   <string>AR PL ZenKai Uni</string>
  </edit>
 </match> 
 <match target="pattern">
  <test qual="any" name="family">
   <string>sans-serif</string>
  </test>
  <edit name="family" mode="prepend" binding="strong">
   <string>Bitstream Vera Sans</string>
   <string>Microsoft YaHei</string>
   <string>DejaVu Sans</string>
   <string>AR PL UMing CN</string>
   <string>AR PL ShanHeiSun Uni</string>
   <string>AR PL UKai CN</string>
   <string>AR PL ZenKai Uni</string>
  </edit>
 </match> 
 <match target="pattern">
  <test qual="any" name="family">
   <string>monospace</string>
  </test>
  <edit name="family" mode="prepend" binding="strong">
   <string>Bitstream Vera Sans Mono</string>
   <string>Microsoft YaHei</string>
   <string>DejaVu Sans Mono</string>
   <string>AR PL UMing CN</string>
   <string>AR PL ShanHeiSun Uni</string>
   <string>AR PL UKai CN</string>
   <string>AR PL ZenKai Uni</string>
  </edit>
 </match> 

</fontconfig>

However when I use the firefox, I found the title of the firefox window is not YaHei.

See the image here

So what is the problem?