Rake tasks to find missing translations by comparing available yml files.

i18n.rb

namespace :i18n do
  task en_bork: :environment do
    I18n.locale = :en

    en = I18n.t(".").except(:faker)
    chef = replace_values!(en) do |val|
      `echo #{val.inspect} | chef`.chomp.sub(/\s*Bork Bork Bork!/m, "")
    end

    File.open(Rails.root + "config/locales/en-bork.yml", "w") do |fd|
      fd.write(YAML.dump("en-bork" => chef.deep_stringify_keys))
    end
  end

  task missing: :environment do
    keys_per_locale = available_locales.map do |locale|
      I18n.locale = locale
      {
        locale => dot_deep_keys(I18n.t(".").except(:faker)).sort
      }
    end.reduce(:merge)

    available_locales.each do |locale|
      (available_locales - [locale]).each do |other|
        d = keys_per_locale[other] - keys_per_locale[locale]
        if d.present?
          puts "Missing from #{locale} but available in #{other}:"
          d.each { |k| puts "  #{k}" }
        end
      end
    end
  end
end

def available_locales
  Dir[Rails.root + "config/locales/*.yml"].map do |fn|
    YAML.load(File.read(fn))
  end.reduce(&:deep_merge).keys.map(&:to_sym)
end

def dot_deep_keys(m, prefix = nil)
  m.keys.map do |k|
    [prefix, k].compact.join(".")
  end + m.select do |_,v|
    Hash === v
  end.map do |k,v|
    dot_deep_keys(v, [prefix, k].compact.join("."))
  end.flatten
end

def replace_values!(val, path = [], &block)
  case val
  when String
    g = val.scan(/%{.*?}/m)
    t = val.scan(/<.*?>/m)

    i = j = 0
    yield(val).gsub(/%{.*?}/m) do |_|
      g[i].tap{ i += 1 }
    end.gsub(/<.*?>/m) do |_|
      t[j].tap{ j += 1 }
    end
  when Hash
    val.each do |k,v|
      next if ["formats"].include?(path[-1])
      val[k] = replace_values!(v, path + [k], &block)
    end
  when Array
    val.map { |v| replace_values!(v, path, &block) }
  else
    val
  end
end