Paypal error for non-English user

My litecart is customized into English and Chinese interface for my customer. Recently it is found that Paypal works fine for English user but it (paypal) shows error message (telling that the charset does not match) if Chinese user wanna pay by paypal. I check on some websites, the solution is to add an additional coding in the checkout page, inside the section:

Does anyone know how should i realize this in LiteCart? Thank you.
The module is already passing this value:

See row 62 in the php code:

        'charset'       => language::$selected['charset'],

What is the charset set to in Admin -> Languages -> Edit Language?
Already set as UTF-8 for chinese, but it doesnt work, so i think i need an extra statement to override the charset setting for paypal
Well the value to override is line 62 in

        'charset'       => language::$selected['charset'],

See HTML Form Basics for PayPal Payments Standard chapter Setting the Character Set — charset.

Big5 (Traditional Chinese in Taiwan)
gb2312 (Simplified Chinese)
HZ-GB-2312 (Traditional Chinese in Hong Kong)