To make my question clearer, here are the details.
1) When double click the CHM file, a message box popped up saying "
2) This occurred on an XP SP3 PC, but not on my Vista SP2 PC where the only language installed is English.
3) On XP SP3 PC, every single HTML file in the RoboHelp project can be displayed without message popping up for installing Chinese language pack. There is really no Chinese involved in this project.
4) The RoboHelp 8 project was upgraded from a previous RoboHelp 6 project. The CHM file from RoboHelp 6 also has this problem
I suspect that if a setting in the project causes this problem and by removing this setting the issue will be gone.
Thanks for the help!