only in patch2:
unchanged:
--- a/core/modules/language/src/Config/LanguageConfigFactoryOverride.php
+++ b/core/modules/language/src/Config/LanguageConfigFactoryOverride.php
@@ -169,7 +169,7 @@ public function createConfigObject($name, $collection = StorageInterface::DEFAUL
    *   The configuration collection name for a langcode.
    */
   protected function createConfigCollectionName($langcode) {
-    return 'language.' . $langcode;
+    return 'language.' . str_replace('-', '_', $langcode);
   }
 
   /**
@@ -192,7 +192,7 @@ protected function getLangcodeFromCollectionName($collection) {
     if (!isset($matches[1])) {
       throw new \InvalidArgumentException(String::format('!collection is not a valid language override collection', array('!collection' => $collection)));
     }
-    return $matches[1];
+    return str_replace('_', '-', $matches[1]);
   }
 
   /**