Get Current Language ISO Code in TYPO3

any.php

<?php

use TYPO3\CMS\Core\Context\Context;
use TYPO3\CMS\Core\Utility\GeneralUtility;

// ...

$context = GeneralUtility::makeInstance(Context::class);

/** @var TYPO3\CMS\Core\Site\Entity\Site */
$site = $GLOBALS['TYPO3_REQUEST']->getAttribute('site');
$langId = $context->getPropertyFromAspect('language', 'id');

/** @var TYPO3\CMS\Core\Site\Entity\SiteLanguage */
$language = $site->getLanguageById($langId);
$langCode = $language->getTwoLetterIsoCode();