codeigniter更改第三方应用程序语言

My thirdparty app comes with languages support in it.
Do I have to 'manually' copy the language folder to 'application/language' ?
Is so, what the use of $autoload['language'] = array('thirdparty'); ?

You need to add the package path to the codeigniter loader:

$this->load->add_package_path(APPPATH.'third_party/foo_bar/');

After you will be able to load it's language file normally:

$this->lang->load('filename', 'language');

Take a look at: CodeIgniter Loader Class