Revert "[TASK] removed deprecated call to compat_version"

This reverts commit 3ba6e51f.

Classes/Service/ConfigurationService.php

@@ -127,11 +127,17 @@ class ConfigurationService extends AbstractService {
 			unset($this->extConfig['viewLanguages']);
 
 			$availableLanguageKeys = [];
-			$languages = explode(
-				'|', TYPO3_languages
-			);
-			foreach ($languages as $language) {
-				$availableLanguageKeys[$language] = TRUE;
+			if (GeneralUtility::compat_version('6.0')) {
+				/** @var Locales $locales */
+				$locales = GeneralUtility::makeInstance('TYPO3\CMS\Core\Localization\Locales');
+				$availableLanguageKeys = $locales->getLanguages();
+			} else {
+				$languages = explode(
+					'|', TYPO3_languages
+				);
+				foreach ($languages as $language) {
+					$availableLanguageKeys[$language] = TRUE;
+				}
 			}
 
 			foreach ($langs as $lang) {