translate a field before rendering
In short: use hook_field_widget_form_alter()

/*
* translate the form
*/
function mymodule_field_widget_form_alter(&amp;$element, &amp;$form_state, $context){

if(isset($element['#title'])){
  $element['#title'] = t($element['#title']);
}
if(isset($element['value']['#title'])){
  $element['value']['#title'] = t($element['value']['#title']);
}
if(isset($element['#description'])){
  $element['#description'] = t($element['#description']);
}
if(isset($element['value']['#description'])){
  $element['value']['#description'] = t($element['value']['#description']);
}
}


This translates titles and edscriptions of textstrings. 

To show the fields title and description in the given language in node_view:

function mymodule_preprocess_field(&amp;$vars) {
if ($node = menu_get_object()){
  if($node-&gt;type == 'immoclient'){
    // Check to be sure there's a label and it's visible.
    if(isset($vars['label']) &amp;&amp; $vars['label_hidden'] === FALSE){
      $vars['label'] = t($vars['label']);
    }
    $field_name = $vars['element']['#field_name'];
    $trans_fields = mymodule_trans_fields();
      if(in_array($field_name, $trans_fields)){
        $items = $vars['items'];
        $result = count($items);
        for($i = 0;$i &lt; $result; $i++){
          $vars['items'][$i]['#markup'] = t($vars['items'][$i]['#markup']) ;
        }
      }
     }
    }
   }


and mymodule_trans_fields() returns an array of fields to translate.

To show the items (and here the answer) in the appropriate language for selects and checkboxes in the form, I used hook_form_FORMID_alter:

function mymodule_form_[mynode_form]_alter(&amp;$form,&amp;$form_state,$form_id){
    foreach($form as $key =&gt; $value){
      $field = strpos($key, 'field_');
        //only for fields!
          if($field !== false){
            if(isset($form[$key]['und']['#description'])){
            //seems so that every field has a description, to use it for items too
            //build variables
              $res = $form[$key]['und'];
              $desc_t = t($form[$key]['und']['#description']);
              $form[$key]['und']['#description'] = $desc_t;
                }
               }
             }
           }