Using khmer language in Birt Report

Yaohaha

Birt report version being used is 4.6.0. PDF file is being generated. I want to use khmer characters in the pdf.

Steps performed :

Download and Install the khmer font being used in the report. Ex : KhmerOSbattambang
Set the Charset of the report to utf-8. Ex : <?xml version="1.0" encoding="UTF-8"?>
Create a text element in the birt report with khmer characters. Ex : គបឈេទ
The xml generated for this text element will be :

<![CDATA[គបឈេទ]]>
Assign the text element to the "KhmerOSbattambang" font.
Preview the generated pdf.
The generated pdf will contain some unwanted special characters instead of the actual khmer characters.

Please let me know the solution for this problem. Thanks in advance.