Is it a base UBE or custom? If base you maybe lucky in that it's already setup. If not you need to get the UBE in a project and then click the VO icon and follow the instructions in the link I pasted.
(You basically change the text of each object in a UBE to Chinese)
What language to display then gets pulled from the users profile
if your default language says lets say "English" (@ user profile) and you want to print in different language say "Chinese", then you need to add a processing option to take language override. There is a system function to override language which needs to be called initially to take required language to print.
What version of JDE?
Do you have the language packs for the selected languages installed in JDE?
Invoices, as your example, should print in the language that is specified for the customer (F0101.ABLNGP)
See the Customer Level Break Header Do section:
// Retrieve the customer's language preference.
F0101 Get Address Information for OP
// Set the language preference.
If VA rpt_szLanguagePreference_LNGP is not equal to VA rpt_szPreviousLanguagePref_LNG And VA rpt_szErrorMessage_DTAI is equal to <Null>
// If language preference is blank, reset to default language.
If VA rpt_szLanguagePreference_LNGP is equal to <Blank>
[B]Set Language Preference[/B](SL LanguagePreference)
[B]Set Language Preference[/B](VA rpt_szLanguagePreference_LNGP)