Autogenerate and autosort missing i18n translation keys for a Rails application while running Cucumber features

hooks.rb

# Put this in features/support/hooks.rb and add i18n-missing_translations and i18n_yaml_sorter to your Gemfile

require 'i18n/missing_translations'
require 'i18n_yaml_sorter'

at_exit do
  require 'yaml'

  data = YAML.load_file('config/locales/en.yml')
  data.deep_merge!(I18n.missing_translations)

  output = StringIO.new(YAML.dump(data))

  File.open('config/locales/en.yml', 'wb') { |fh| fh.puts I18nYamlSorter::Sorter.new(output).sort }
end