I tried to install the simplified chinese for the frontend of Joomla 1.5: file language_1510_zhCN.zip, with subdirectory zh-CN.

At installation Joomla kept complaining about a missing file gbsn00lp.php. It turned out that the language pack installation file (zh-install.xml) mentions this file inside the fonts tag with two other files: gbsn00lp.z and gbsn00lp.ctg.z.

These three files are pdf fonts. My site does not use the PDF option, so I uncommented these fonts and I was able to install the language pack.

The three files can be commented out like this:

 
<fonts> <!--
  <filename>gbsn00lp.php</filename>
  <filename>gbsn00lp.z</filename>
  <filename>gbsn00lp.ctg.z</filename>
 -->
</fonts>