Migrate two user fields (translation) to translation
Now it works.  There was a problem with the migration of the user admin (user/1). If you migrate admin user, then you can't edit translations of any user. 
Now I put a custom source plugin with function query() overwritten:

/**
   * {@inheritdoc}
   */
  public function query() {

    $query = parent::query();

   // Only migrate users not admin (1)
    $query-&gt;condition('uid', '1', '&lt;&gt;');
    return $query;
  }