[BUGFIX] Fill alternative language keys correctly

This change adds the language dependencies individually to the array
instead of completely overwriting them as a string. Since the
dependencies are iterated in the core, this function only adds to the
array instead of overwriting the first index.

Resolves: #88045
Releases: master, 9.5
Change-Id: I3101bf8f9873ffa5ceeee3cc9e9ace36858f39a4
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/60356


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: theline <typo3@theline.capella.uberspace.de>
Tested-by: Benjamin Kott <benjamin.kott@outlook.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: theline <typo3@theline.capella.uberspace.de>
Reviewed-by: Benjamin Kott <benjamin.kott@outlook.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>

typo3/sysext/extbase/Classes/Utility/LocalizationUtility.php

@@ -199,7 +199,7 @@ class LocalizationUtility
             $locales = GeneralUtility::makeInstance(Locales::class);
             if (in_array($languageKeys['languageKey'], $locales->getLocales())) {
                 foreach ($locales->getLocaleDependencies($languageKeys['languageKey']) as $language) {
-                    $languageKeys['alternativeLanguageKeys'] = $language;
+                    $languageKeys['alternativeLanguageKeys'][] = $language;
                 }
             }
         } elseif (!empty($GLOBALS['BE_USER']->uc['lang'])) {