Entity translation fields... how to map?

I've a problem with my d7 to d7 migrate... i've tried to assign a variable like this:

class MigrazioneNodiCategorie extends MigrazioneNodi{
  public function __construct(array $arguments){
    parent::__construct($arguments);

    $this->sourceFields['title_field:language'] = 'titolo';
    $this->source = new MigrateSourceSQL($this->query(), $this->sourceFields, NULL, $this->sourceOptions);

    $this->addFieldMapping('title_field', 'title_field');
    $this->addFieldMapping('title_field:language', 'title_field:language');

but the imported language are IT or random, it doesn't create the correct multi language fields... how can I map this fields correctly?

thanks