Alter the Language Switcher block HTML

Is it possible to alter/modify the HTML in the Language Switcher block?
If I do

function phptemplate_preprocess_block(&$vars) {
  if ($vars['block']->module == "locale") {
      print_r($vars);
    }
  }

in the template.php file i get all variables of the block, but I cannot alter the HTML created by the Internatialization module here (which is in $block->content).

Is there any function for editing that HTML? A theme function perhaps?