How to translate the category names in the manager?

<?php
/**
		set for event: OnResourceTVFormRender:
			'categories' => &$finalCategories,
            'template' => $templateId,
            'resource' => $this->resource->get('id'),
            'tvCounts' => &$this->tvCounts,
            'hidden' => &$hidden,

			
**/
$eventName = $modx->event->name;
switch($eventName) {
    case 'OnResourceTVFormRender':
                $lexiconname = empty($lexiconname)?'website':$lexiconname;

                $modx->getService('lexicon','modLexicon');
                $modx->lexicon->load($lexiconname.':default');

                foreach($categories as $id=>$aCategory)
                {
                        //translate category name
                        $aCategoryName = $modx->lexicon($aCategory['category']);

		/** the following line does not work :-(
		  the new values in $categories seams correct but when coming back to manager/controllers/default/resource/resource.class.php,
		  $finalCategories is not updated... 
		**/
                        $categories[$id]['category'] = $aCategoryName;
                }
        break;
}
return;

$aCategoryName = $modx->lexicon($aCategory);