Traductor (rails models translations)

translatable.rb

module Translatable
  extend ActiveSupport::Concern

  included do
    translation_class_name = "Translations::#{model_name}Translation"

    has_many :translations,
             class_name: translation_class_name,
             dependent: :delete_all,
             inverse_of: model_name.to_s.underscore.to_sym

    has_one :current_translation,
            -> { where(locale: I18n.locale) },
            class_name: translation_class_name,
            inverse_of: model_name.to_s.underscore.to_sym

    # always include translations if translatable
    default_scope -> { includes(:current_translation) }
  end
end

translation.rb

# Translation model (connected to translatable model)
module Translation
  extend ActiveSupport::Concern

  included do
    # converts `Translations::CityTranslation` to `city`
    translatable_name = model_name.to_s.split('::').last.chomp('Translation').to_s.underscore

    belongs_to translatable_name.to_sym, inverse_of: :translations

    validates :locale,
              presence: true,
              length: { is: 2 }

    validates "#{translatable_name}_id",
              presence: true
  end
end