There is no problem in storing 5 languages.
The database will only store in the Locale set by DB_LOCALE at database creation time.
So, if you set your DB_LOCALE to en_us.utf-8, then create a database, you're good to go.
You CLIENT_LOCALE however, is only necessary to display what you have stored. If you set your CLIENT_LOCALE to utf-8, you need an application that can handle utf-8.
A terminal program like dbaccess can't.
If you can set you CLIENT_LOCALE to a chinese locale, the database server will translate the UTF-8 codese to chinese and you 'chinese enabled' application will have no problems storing.
How to change your keyboard?
That depends on what os you are.