Simple Form with doctrine knp translatable extentions

I'm searching for a simple way to edit translated fields within a symfony2 form. I'm using the doctrine knp translatable extentions for translation of the entity. The form mixes not translated with translated properties in a special order. The form should be displayed (end edit) only in the active language. For example:

 $builder
 ->add('key')
 ->add('translate1','text',array(
    'property_path' => 'translations[de].translate1',
 ))
 ->add('mynumber')
 ->add('translate2','text',array(
    'property_path' => 'translations[de].translate2',
))

If the language translations[de] does not exists i get an error: "Cannot read property "translate1" from an array... "

A2LiX Translation Form is not the solution, because it displays all translatabe fields in a single list.

Any ideas?