i18n.rb

# config/initializers/i18n.rb

# chain the translations usage tracker into the i18n backend

require File.expand_path('../../../lib/i18n/backend/track_usage', __FILE__)

I18n.backend = I18n::Backend::Chain.new(I18n::Backend::TrackUsage.new, I18n.backend)

track_usage.rb

# lib/i18n/backend/track_usage.rb

module I18n
  module Backend
    class TrackUsage

      def reload!
        path = File.expand_path('../../../../log/translations.log', __FILE__)
        file = File.open(path, 'a')
        file.sync = true
        @logger = Logger.new(file)
        nil
      end

      def translate(*args)
        @logger.info ([Time.now] + args) * ' '
        nil
      end

      def localize(*args)
        nil
      end

      def available_locales
        nil
      end

    end
  end
end

translations.rake

# lib/tasks/translations.rake

task :translations do
  # read log
  path = File.expand_path('../../../log/translations.log', __FILE__)
  lines = File.read(path).split("\n")
  
  # aggregate
  stats = Hash.new { |h, k| h[k] = 0 }
  pattern = /(\d{4}-\d\d-\d\d \d\d:\d\d:\d\d \+\d{4}) (\w\w) ([\w.]+) ({.*})/
  lines.each do |line|
    _, time, locale, key, opts = line.match(pattern).to_a
    stats[key] += 1 unless key.nil?
  end
  
  # sort
  sorted = stats.to_a.sort_by { |a| a.last }.reverse
  w2 = sorted.first.last.to_s.length

  # fetch keys from locale files and add with 0
  locales = I18n.available_locales
  locales.each do |locale|
    nested = { locale => I18n.backend.translate(locale, '') }
    c = Class.new.tap { |t| t.extend(I18n::Backend::Flatten) }
    flat = c.flatten_translations(locale, nested, true, false)
    flat.each do |key, value|
      key = key.to_s[3..-1] # slice locale
      if stats[key] == 0
        sorted << [key, 0]
      end
    end
  end

  w1 = sorted.size.to_s.length

  # output
  sorted.each_with_index do |e, index|
    puts "% #{w1}s\t% #{w2}s\t%s" % ([ index+1 ] + e.reverse)
  end
end