A locale is what defines the language, encoding, etc on your system.
To know the default locale(s) of your system, go to /var/lib/locales/supported.d/:
you should have, at least:
which defines the default locale.
List installed locales
To list the locales already installed on your computer, open a terminal:
Add a locale
To add chinese from China Mainland locale, open a terminal:
sudo locale-gen zh_CN.UTF-8
Ubuntu documentation has a page for locales management.