we are *sure* we want to set the encoding, so silence warnings around it

railties/lib/rails.rb

@@ -22,8 +22,10 @@ require 'action_dispatch/railtie'
 if RUBY_VERSION < '1.9'
   $KCODE='u'
 else
-  Encoding.default_external = Encoding::UTF_8
-  Encoding.default_internal = Encoding::UTF_8
+  silence_warnings do
+    Encoding.default_external = Encoding::UTF_8
+    Encoding.default_internal = Encoding::UTF_8
+  end
 end
 
 module Rails

railties/lib/rails/application/configuration.rb

@@ -1,4 +1,5 @@
 require 'active_support/core_ext/string/encoding'
+require 'active_support/core_ext/kernel/reporting'
 require 'rails/engine/configuration'
 
 module Rails
@@ -53,8 +54,10 @@ module Rails
       def encoding=(value)
         @encoding = value
         if "ruby".encoding_aware?
-          Encoding.default_external = value
-          Encoding.default_internal = value
+          silence_warnings do
+            Encoding.default_external = value
+            Encoding.default_internal = value
+          end
         else
           $KCODE = value
           if $KCODE == "NONE"