_plugins/translate.rb

# This file is licensed under the MIT License (MIT) available on
# http://opensource.org/licenses/MIT.

#translate( id [,category ,lang] )
#Return translated string using translations files

#category and lang are set to current page.id and page.lang, but they can
#also be set manually to get translations for global layout and urls.
#Example: {% translate button-wallet layout %} will return the
#translated button-wallet string for the global layout file

#dynamic variables can be used as arguments
#Example: {% translate menu-{{id}} %}

#urls and anchors are automatically replaced and translated. 
#Example: #vocabulary##[vocabulary.wallet] is replaced by
#/en/vocabulary#wallet when the page is in english or
#/fr/vocabulaire#porte-monnaie when the page is in french.

require 'yaml'
require 'cgi'

module Jekyll

  class TranslateTag < Liquid::Tag

    def initialize(tag_name, id, tokens)
      super
      @id = id
    end

    def render(context)
      #Load translations
      site = context.registers[:site].config
      if !site.has_key?("loc")
        site['loc'] = {}
        Dir.foreach('_translations') do |file|
          next if file == '.' or file == '..'
          lang=file.split('.')[0]
          site['loc'][lang] = YAML.load_file('_translations/' file)[lang]
        end
      end
      #define id, category and lang
      defaulten = true
      lang = Liquid::Template.parse("{{page.lang}}").render context
      cat = Liquid::Template.parse("{{page.id}}").render context
      id=@id.split(' ')
      if !id[1].nil?
        cat = Liquid::Template.parse(id[1]).render context
      end
      if !id[2].nil?
        lang = Liquid::Template.parse(id[2]).render context
        defaulten = false
      end
      id=Liquid::Template.parse(id[0]).render context
      if lang == ''
        lang = 'en'
      end
      #get translated string
      text = ''
      keys = cat.split('.')
      ar = site['loc'][lang]
      #recursive loop to handle cases where category is like "anchor.vocabulary"
      for key in keys do
        break if !ar.is_a?(Hash) || !ar.has_key?(key) || !ar[key].is_a?(Hash)
        ar = ar[key]
      end
      if ar.has_key?(id) && ar[id].is_a?(String)
        text = ar[id]
      end
      #fallback to English if string is empty
      if text == '' and defaulten == true
        lang = 'en'
        ar = site['loc'][lang]
        for key in keys do
          break if !ar.is_a?(Hash) || !ar.has_key?(key) || !ar[key].is_a?(Hash)
          ar = ar[key]
        end
        if ar.has_key?(id) && ar[id].is_a?(String)
          text = ar[id]
        end
      end
      #interpret Liquid templating in string
      text = Liquid::Template.parse(text).render context

      #replace urls and anchors in string
      url = site['loc'][lang]['url']
      url.each do |key,value|
        if !value.nil?
          text.gsub!("#" key "#",'/' lang '/' CGI::escape(value))
        end
      end

      ## Hack for renaming links to the Bitcoin paper. Safe to remove
      ## when all languages have "bitcoin-paper:" defined in the "url:"
      ## section of their '_translations' YAML file.
      text.gsub!('#bitcoin-paper#','/bitcoin.pdf')

      anc = site['loc'][lang]['anchor']
      anc.each do |page,anch|
        anch.each do |key,value|
          if !value.nil?
            text.gsub!("[" page '.' key "]",CGI::escape(value))
          end
        end
      end
      text
    end
  end

end

Liquid::Template.register_tag('translate', Jekyll::TranslateTag)