TCA::insertCountries() 

\nn\t3::TCA()->insertCountries($config, $a = NULL); 

Inserts list of countries into a TCA. Alias to nnt3::Flexform->insertCountries( $config, $a = null ); Description and further examples there.

Example in the TCA:

'config' => [
    'type' => 'select',
    'itemsProcFunc' => 'nn\t3\Flexform->insertCountries',
    'insertEmpty' => true,
]

| @return array

public function insertCountries( $config, $a = null )
{
	return \nn\t3::Flexform()->insertCountries( $config, $a );
}