Align admin progress bars form fields with new translations interface

Add new js method to recover selected language to disable correctly default language fields.

app/assets/javascripts/forms.js.coffee

@@ -40,7 +40,8 @@ App.Forms =
   hideOrShowFieldsAfterSelection: ->
     $("[name='progress_bar[kind]']").on
       change: ->
-        title_field = $("[name^='progress_bar'][name$='[title]']").parent()
+        locale = App.Globalize.selected_language()
+        title_field = $(".translatable-fields[data-locale=#{locale}]")
 
         if this.value == "primary"
           title_field.hide()

app/assets/javascripts/globalize.js.coffee

@@ -1,5 +1,8 @@
 App.Globalize =
 
+  selected_language: ->
+    $("#select_language").val()
+
   display_locale: (locale) ->
     App.Globalize.enable_locale(locale)
     App.Globalize.add_language(locale)