A cached key-value store backend for Rails I18n. Designed to speed up translations when using a database like Redis or Mongo.

application_controller.rb

class ApplicationController < ActionController::Base
  before_filter :ensure_fresh_i18n
  
  private
  def ensure_fresh_i18n
    I18n.backend.ensure_freshness! I18n.locale
  end
end

cached_key_value_store.rb

module I18n
  module Backend
    class CachedKeyValueStore < KeyValue
      include Memoize

      KEY_PREFIX = 'i18n:locale_version:'

      def store_translations(locale, data, options = {})
        update_version! locale
        super
      end

      def ensure_freshness!(locale)
        current = current_version locale

        if last_version[locale] != current
          reset_memoizations! locale
          last_version[locale] = current
        end
      end

      def last_version
        @last_version ||= {}
      end

      def update_version!(locale)
        @store["#{KEY_PREFIX}#{locale}"] = Time.now.to_i
      end

      def current_version(locale)
        @store["#{KEY_PREFIX}#{locale}"]
      end
    end
  end
end

cached_key_value_store_spec.rb

require 'spec_helper'

describe I18n::Backend::CachedKeyValueStore do
  let(:store) { {} }
  subject { I18n::Backend::CachedKeyValueStore.new(store) }

  describe '#ensure_freshness!' do
    context 'with expired locale' do
      before do
        store['i18n:locale_version:en'] = '2'
      end

      it 'calls reset_memoizations!' do
        subject.should_receive(:reset_memoizations!).with(:en)
        subject.ensure_freshness! :en
      end

      it 'updates last_locale' do
        subject.ensure_freshness! :en
        subject.last_version.should == { en: '2' }
      end
    end

    context 'with current locale' do
      before do
        store['i18n:locale_version:en'] = '1'
        subject.last_version[:en] = '1'
      end

      it 'does not call reset_memoizations!' do
        subject.should_not_receive(:reset_memoizations!)
        subject.ensure_freshness! :en
      end

      it 'maintains last_locale' do
        subject.ensure_freshness! :en
        subject.last_version.should == { en: '1' }
      end
    end
  end

  describe 'store_translations' do
    before do
      store['i18n:locale_version:en'] = '2'
    end

    it 'updates and dememoizes' do
      subject.should_receive(:reset_memoizations!).with(:en)
      subject.store_translations(:en, {simple: 'test'})
      subject.current_version(:en).should_not ==  '2'
      store['en.simple'].should match(/test/)
    end
  end
end

initialize_i18n.rb

I18n.backend = I18n::Backend::CachedKeyValueStore.new($redis)