[Translation] Added search to FallbackLocale Catalogue.

When the current locale catalogue doesn't contain the id searched, the code doesn't search in the fallbacklocale catalogue (as is explained in the documentation).
Added the search to the fallbacklocale catalogue to the translation function.

src/Symfony/Component/Translation/Translator.php

@@ -112,6 +112,15 @@ class Translator implements TranslatorInterface
             $this->loadCatalogue($locale);
         }
 
+        if(!$this->catalogues[$locale]->has($id, $domain)) {
+            
+            $locale = $this->fallbackLocale;
+            
+            if (!isset($this->catalogues[$locale])) {
+                $this->loadCatalogue($locale);
+            }
+        } 
+
         return strtr($this->catalogues[$locale]->get($id, $domain), $parameters);
     }