Twitter Date Picker localized on front and with only ISO sent/retrieved from the server

_form.html.haml

= f.input :date_of_birth, as: :date_picker

application.html.haml

!!! 5
%html(lang="en")
  %head
    %meta(charset="utf-8")
    
    / ...
    
    :javascript
      window.CurrentLocale = "#{I18n.locale}";

application.js.coffee

#= require bootstrap-datepicker/js/bootstrap-datepicker
#= require bootstrap-datepicker/js/locales/bootstrap-datepicker.fr
#= require moment/min/moment.min
#= require moment/min/lang/fr

$(document).ready ->

  moment.lang(window.CurrentLocale)

  $(".datepicker").each (i, field) ->
    $(field).val(moment($(field).val()).format('L'))

  $(".datepicker").datepicker
      language: window.CurrentLocale
    .on "changeDate", (en) ->
      $(this).next("input[type=hidden]").val(moment(en.date).format("YYYY-MM-DD"))

date_picker_input.rb

class DatePickerInput < SimpleForm::Inputs::Base
  def input
    res = ""
    res << @builder.text_field(attribute_name, input_html_options.merge(name: nil, class: "datepicker"))
    res << @builder.hidden_field(attribute_name, id: "#{attribute_name}_hidden")

    res.html_safe
  end
end