Merge branch '4.4' into 5.1

* 4.4:
  [ErrorHandler] Return false directly and remove unused variable
  [OptionsResolver] Assert that the error type is valid in deprecations test
  [HttpClient] Allow bearer token with colon
  [Form] Fix custom formats deprecation with HTML5 widgets
  [Translator] Optional Intl dependency
  [Contracts][Translation] Optional Intl dependency
  [ErrorHandler] Escape JSON encoded log context
  update missing translations arabic
  [Yaml] simplify the test
  fix test by letting mock throw the actual expected exception

Translator.php

@@ -150,15 +150,15 @@ public function addResource(string $format, $resource, string $locale, string $d
     public function setLocale(string $locale)
     {
         $this->assertValidLocale($locale);
-        $this->locale = $locale;
+        $this->locale = $locale ?? (class_exists(\Locale::class) ? \Locale::getDefault() : 'en');
     }
 
     /**
      * {@inheritdoc}
      */
     public function getLocale()
     {
-        return $this->locale ?? \Locale::getDefault();
+        return $this->locale;
     }
 
     /**