I just discovered a very handy api to import taxonomy.
It is included with the taxonomy csv module in the file taxonomy_csv.api.inc

I needed to do something very simple import some terms into a vocabulary (no hierarchy, no related terms, just tags..). I already had my csv parser to create my nodes so I did not use the interface of the module. Since I had my terms in an array I just needed to prepare them and import them with this api function :

  //prepare
  $terms = array(
    array('name' => $data[20]),