Thanks @APMuthu.
I actually added it to lang/installed_languages.inc to lang/installed_languages.inc as follows. But it does not work since the language is used before a user is logged in, therefore the user_theme() does not work here. The reason of using the user_theme() is when dashboard theme is used and the encoding is utf-8, some of the wordings (legends, headers) on the charts or tables disappeared. The missing wordings will show up when the encoding is set to "iso-8859-1". Would you suggest any other work around where I could use utf-8 to handle my chinese character inputs and it does not affect the dashboard charts... Thank you.
include_once($path_to_root . "/includes/current_user.inc");
//$themename=user_theme();
$themename="dashboard";
if ($themename=='dashboard')
{
$encoding_0="iso-8859-1";
//$encoding_0="utf-8";
}
else
{
$encoding_0="utf-8";
//$encoding_0="iso-8859-1";
}
$installed_languages = array (
0 =>
array (
'code' => 'C',
'name' => 'English',
'encoding' => $encoding_0,
),