Update translation.rst

book/translation.rst

@@ -428,6 +428,14 @@ via the ``request`` object::
 
         $request->setLocale('en_US');
     }
+
+.. note::
+
+    Setting the locale using the ``$request->setLocale()`` method won't affect 
+    rendering in the same action. The translator locale is set during the
+    kernel.request event. Either set the locale before the listener is called
+    (e.g. in a custom listener) or use the ``setLocale()`` method of the 
+    ``translator`` service.
 
 .. tip::