rspec_i18n_helper.rb

module I18nHelper
  def i18n
    ChainableTranslation.new
  end

  class ChainableTranslation
    attr_reader :options

    def initialize(scopes = [], options = {})
      @scopes = Array(scopes)
      @options = options
    end

    def to_s(options = {})
      scope = @scopes.join('.')
      I18n.t scope, self.options.deep_merge(options)
    end
    
    alias_method :+, :to_s
    
    def +@
      to_s
    end
    
    def locale=(locale)
      to_s locale: locale
    end
    
    def [](*scope, scope_or_options)
      result = if scope_or_options.respond_to? :to_hash
        __chain_i18n_options__ scope_or_options.to_hash
      else
        __chain_i18n_scope__ scope_or_options
      end

      result.__chain_i18n_scope__ scope
    end

    def method_missing(scope)
      __chain_i18n_scope__ scope
    end

    def respond_to?(*)
      true
    end
    
    def __chain_i18n_scope__(scope)
      self.class.new @scopes + Array(scope), self.options
    end
    
    def __chain_i18n_options__(options)
      self.class.new @scopes, self.options.deep_merge(options)
    end
  end
end

RSpec.configure do |c|
  c.include I18nHelper
end

zzz-example.rb

# Normal use:
i18n.models.chicken.flap.to_s ==
  I18n.t('models.chicken.flap')

# I18n params are passed through:
i18n.models.chicken.scratch_a.to_s(object: i18n.objects.dirt) ==
  I18n.t('models.chicken.scratch_a', object: i18n.objects.dirt)

# Interpolate easily
farmer = Farmer.first

%w(dog rooster hen).map { |animal| i18n.models[animal].greeting + { subject: farmer.name } } ==
  %w(dog rooster hen).map { |animal| I18n.t("models.#{animal}.greeting", subject: farmer.name) }

# Use interpolation to get around edge cases, like nested modules:
+i18n.models['admin/tyson_hq'].district ==
  I18n.t('models.admin/tyson_hq.district')