link_lang.rb

# use: {% link about.html %}

module Jekyll

  class LinkLang < Liquid::Tag

    def initialize(tag_name, link, tokens)
      super
      @link = link.strip
    end

    def render(context)
      @context = context
      find(@link)
    end

    private

    def find(link)
      language = @context.registers[:page]["language"]
      @context.registers[:site].pages.each do |page|
        if page.respond_to?(:language)
          if page.language == language && page.name == link
            return page.url
          end
        end
      end
    end

  end
end

Liquid::Template.register_tag('link_lang', Jekyll::LinkLang)