Magento 2 – How to Get Country Name from Country Code

Try like that (in some phtml file, but you can rearange it to fit only in your php function):

<ul>
  <?php foreach(Mage::app()->getWebsites() as $website): ?>
    <?php foreach ($website->getGroups() as $group): ?>
      <?php $stores = $group->getStores();
        foreach ($stores as $store): ?>
        <li class="<?php echo Mage::app()->getStore($store->getStoreId())->getCode();?>"><a href="<?php echo Mage::app()->getStore($store->getStoreId())->getBaseUrl(Mage_Core_Model_Store::URL_TYPE_LINK);?>"></a></li>
      <?php endforeach; ?>
    <?php endforeach; ?>
  <?php endforeach; ?>
  </ul>

Now, with $store->getStoreId() you are able to get the store id.

Use below code:

    protected $logger;

    protected $objectManager;

    protected $_curl;

    public function __construct(
    \Psr\Log\LoggerInterface $logger, 
    \Magento\Framework\ObjectManagerInterface $objectManager,
    \Magento\Framework\HTTP\Client\Curl $curl) {
        $this->logger = $logger;
        $this->_curl = $curl;
        $this->objectManager = $objectManager;
    }

    public function getCountryName() {
        $visitorIp = $this->getVisitorIp();
        $url = "freegeoip.net/json/".$visitorIp;
        $this->_curl->get($url);
        $response = json_decode($this->_curl->getBody(), true);
        $countryName = $response['country_name'];
        $stateName = $response['region_name'];
       return $stateName;        
    }

    function getVisitorIp() {       
        $remoteAddress = $this->objectManager->create('Magento\Framework\HTTP\PhpEnvironment\RemoteAddress');
        return $remoteAddress->getRemoteAddress();
    }