[FrameworkBundle][config] allow multiple fallback locales.

Author: aitboudad

reference/configuration/framework.rst

@@ -48,7 +48,7 @@ Configuration
     * :ref:`enabled <profiler.enabled>`
 * `translator`_
     * :ref:`enabled <translator.enabled>`
-    * `fallback`_
+    * `fallbacks`_
 * `validation`_
     * `cache`_
     * `enable_annotations`_
@@ -526,10 +526,10 @@ enabled
 
 Whether or not to enable the ``translator`` service in the service container.
 
-fallback
-........
+fallbacks
+.........
 
-**type**: ``string`` **default**: ``en``
+**type**: ``string|array`` **default**: ``en``
 
 This option is used when the translation key for the current locale wasn't found.
 
@@ -676,7 +676,7 @@ Full default Configuration
             # translator configuration
             translator:
                 enabled:              false
-                fallback:             en
+                fallbacks:            [en]
 
             # validation configuration
             validation: