Locales.yaml

# config/locales/en.yml

en:
  exception:
    show:
      not_found:
        title: "Not Found"
        description: "The page you were looking for does not exists."
      internal_server_error:
        title: "Internal Server Error"
        description: "Sorry, something went wrong while processing your request."
      bad_request:
        title: "Bad Request"
        description: "The server did not understand your request. It may have been malformed."
        bad_taste:
          title: "Bad Taste"
          description: "Sorry, the server thinks you've got a bad taste for food (%{exception_message})."

Ruby.rb

# config/environments/development.rb

config.consider_all_requests_local = false # true

# config/application.rb

config.exceptions_app = ->(env) { ExceptionController.action(:show).call(env) }
config.action_dispatch.rescue_responses["BadTaste"] = :bad_request

# app/controllers/exception_controller.rb

class ExceptionController < ActionController::Base
  layout 'application'

  def show
    @exception       = env['action_dispatch.exception']
    @status_code     = ActionDispatch::ExceptionWrapper.new(env, @exception).status_code
    @rescue_response = ActionDispatch::ExceptionWrapper.rescue_responses[@exception.class.name]

    respond_to do |format|
      format.html { render :show, status: @status_code, layout: !request.xhr? }
      format.xml  { render xml: details, root: "error", status: @status_code }
      format.json { render json: {error: details}, status: @status_code }
    end
  end

  protected

  def details
    @details ||= {}.tap do |h|
      I18n.with_options scope: [:exception, :show, @rescue_response], exception_name: @exception.class.name, exception_message: @exception.message do |i18n|
        h[:name]    = i18n.t "#{@exception.class.name.underscore}.title", default: i18n.t(:title, default: @exception.class.name)
        h[:message] = i18n.t "#{@exception.class.name.underscore}.description", default: i18n.t(:description, default: @exception.message)
      end
    end
  end
  helper_method :details

end

# app/controllers/articles_controller.rb

class ArticlesController < ApplicationController
  def show
    # ...
    raise BadTaste, "Clams are grose" if @article.title =~ /vongole/i
  end
  # ...
  class ::BadTaste < ::StandardError; end
end

Templates.html.erb

<!-- app/views/exception/show.htm.erb -->

<div class="box">
  <h1><%= details[:name] %></h1>
  <p><%= details[:message] %></p>
  <%= link_to "Back to home", root_path %>
</div>