Merge branch '2.8' into 3.1

* 2.8:
  [TwigBridge] fix tests
  Tag the FormFieldRegistry as being internal
  [Form] Fix Date\TimeType marked as invalid on request with single_text and zero seconds
  [Validator] Added missing swedish translation
  [TranslationDebug] workaround for getFallbackLocales.
  [Translation] fixed nested fallback catalogue  using multiple locales.
  fixed phpdoc
  [Command] Fixed method comments as phpDoc syntax
  Added single quotes for upgrade guides.

Author: fabpot

Command/TranslationDebugCommand.php

@@ -21,6 +21,8 @@
 use Symfony\Component\Translation\Catalogue\MergeOperation;
 use Symfony\Component\Translation\MessageCatalogue;
 use Symfony\Component\Translation\Translator;
+use Symfony\Component\Translation\DataCollectorTranslator;
+use Symfony\Component\Translation\LoggingTranslator;
 
 /**
  * Helps finding unused or missing translation messages in a given locale
@@ -295,7 +297,7 @@ private function loadFallbackCatalogues($locale, $transPaths, TranslationLoader
     {
         $fallbackCatalogues = array();
         $translator = $this->getContainer()->get('translator');
-        if ($translator instanceof Translator) {
+        if ($translator instanceof Translator || $translator instanceof DataCollectorTranslator || $translator instanceof LoggingTranslator) {
             foreach ($translator->getFallbackLocales() as $fallbackLocale) {
                 if ($fallbackLocale === $locale) {
                     continue;