wp_can_install_language_pack

function wp_can_install_language_pack() {
	if ( ! wp_is_file_mod_allowed( 'can_install_language_pack' ) ) {
		return false;
	}

	require_once ABSPATH . 'wp-admin/includes/class-wp-upgrader.php';
	$skin     = new Automatic_Upgrader_Skin;
	$upgrader = new Language_Pack_Upgrader( $skin );
	$upgrader->init();

	$check = $upgrader->fs_connect( array( WP_CONTENT_DIR, WP_LANG_DIR ) );

	if ( ! $check || is_wp_error( $check ) ) {
		return false;
	}

	return true;
}