Show i18n keys when locale is "translate"

i18n.rb

# config/initializers/i18n.rb

I18n::Backend::Simple.include(I18n::Backend::TranslateLocale)

translate_locale.rb

# lib/i18n/backend/translate_locale.rb

module I18n
  module Backend
    # Backend that prints the locale key if the current locale is "translate".
    #
    # Include it in your i18n backend in an initializer like so:
    #
    #     I18n::Backend::Simple.include(I18n::Backend::TranslateLocale)
    module TranslateLocale
      IGNORED_KEYS = %w(
        i18n.transliterate.rule
        number.currency.format
        number.format
        number.human.decimal_units.units
        number.human.format
        number.percentage.format
        number.precision.format
      ).freeze

      def translate(locale, key, options = {})
        return super unless locale == :translate &&
                            !options[:default].kind_of?(Hash)

        full_key = [Array(options[:scope]), key].flatten.compact.join(".")

        return super if IGNORED_KEYS.include?(full_key)

        short_options = options.except(
          :fallback,
          :fallback_in_progress,
          :default
        )

        if short_options.any?
          strings = short_options.map { |k, v| "#{k}: #{v.inspect}" }
          details = " (#{strings.join(', ')})"
        end

        "#{full_key}#{details}"
      end
    end
  end
end