I18n: How to check if a translation key/value pairs is missing?

Question

I am using Ruby on Rails 3.1.0 and the I18n gem. I (am implementing a plugin and) I would like to check at runtime if the I18n is missing a translation key/value pairs and, if so, to use a custom string. That is, I have:

validates :link_url,
  :format     => {
    :with => REGEX,
    :message  => I18n.t(
      'custom_invalid_format',
      :scope => 'activerecord.errors.messages'
  )
}

If in the .yml file there is not the following code

activerecord:
  errors:
    messages:
      custom_invalid_format: This is the test error message 1

I would like to use the This is the test error message 2. Is it possible? If so, how can I make that?

BTW: For performance reasons, is it advisable to check at runtime if the translation key/value pairs is present?

Answer 1

You could pass a :default parameter to I18n.t:

I18n.t :missing, :default => 'Not here'
# => 'Not here'

You can read more about it here.

Answer 2

I just had the same question and I want to compute an automatic string in case the translation is missing. If I use the :default option I have to compute the automatic string every time even when the translation is not missing. So I searched for another solution.

You can add the option :raise => true or use I18n.translate! instead of I18n.translate. If no translation can be found an exception is raised.

begin
  I18n.translate!('this.key.should.be.translated', :raise => true) 
rescue I18n::MissingTranslationData
  do_some_resource_eating_text_generation_here
end

Answer 3

I don't know how to this at runtime but you can use rake to find it out. You'll have create your own rake task for that. Here's one:

namespace :i18n do
  desc "Find and list translation keys that do not exist in all locales"
  task :missing_keys => :environment do

    def collect_keys(scope, translations)
      full_keys = []
      translations.to_a.each do |key, translations|
        new_scope = scope.dup << key
        if translations.is_a?(Hash)
          full_keys += collect_keys(new_scope, translations)
        else
          full_keys << new_scope.join('.')
        end
      end
      return full_keys
    end

    # Make sure we've loaded the translations
    I18n.backend.send(:init_translations)
    puts "#{I18n.available_locales.size} #{I18n.available_locales.size == 1 ? 'locale' : 'locales'} available: #{I18n.available_locales.to_sentence}"

    # Get all keys from all locales
    all_keys = I18n.backend.send(:translations).collect do |check_locale, translations|
      collect_keys([], translations).sort
    end.flatten.uniq
    puts "#{all_keys.size} #{all_keys.size == 1 ? 'unique key' : 'unique keys'} found."

    missing_keys = {}
    all_keys.each do |key|

      I18n.available_locales.each do |locale|
        I18n.locale = locale
        begin
          result = I18n.translate(key, :raise => true)
        rescue I18n::MissingInterpolationArgument
          # noop
        rescue I18n::MissingTranslationData
          if missing_keys[key]
            missing_keys[key] << locale
          else
            missing_keys[key] = [locale]
          end
        end
      end
    end
    puts "#{missing_keys.size} #{missing_keys.size == 1 ? 'key is missing' : 'keys are missing'} from one or more locales:"
    missing_keys.keys.sort.each do |key|
      puts "'#{key}': Missing from #{missing_keys[key].join(', ')}"
    end
  end
end

put the given in a .rake file in your lib/tasks directory and execute:

rake i18n:missing_keys 

Information source is here and code on github here.