Add test to ensure English localization is working.

A common mistake for translators is to forget to change the YAML file's
root key from en to their own locale (as people tend to use the English
file as template for a new translation).

spec/requests/rails_admin_spec.rb

@@ -11,4 +11,16 @@
     end
   end
 
+  # A common mistake for translators is to forget to change the YAML file's
+  # root key from en to their own locale (as people tend to use the English
+  # file as template for a new translation).
+  describe "localization" do
+    it "should default to English" do
+      get rails_admin_dashboard_path
+
+      response.should contain("Site administration")
+      response.should contain("Dashboard")
+    end
+  end
+
 end