TYPO3 $GLOBALS['LANG']

I use TYPO3 4.5. Need to get the text of label TCA record, in extention class. I use $ GLOBALS [ 'LANG'] -> sL ($ label). When I logged in BE GLOBALS [ 'LANG'] is object nad all ok. But when logged out, $ GLOBALS [ 'LANG'] = NULL in rerult have error. How to make $ GLOBALS [ 'LANG'] = not null, when I logget out?

my code:

    public function getСolumnValueTca($table,$column,$uid){

    if ($column && $table) {
        $output = null;
        //-----------------------------------
        if ($uid){
            //Ищем нужную запись
            foreach($TCA[$table]['columns'][$column]['config']['items'] as $key => $value){
                if($value['1'] == $uid){
                    $label = $TCA[$table]['columns'] [$column]['config']['items'][$key]['0'];
                    break;
                }
            }
            //------------------------------------------------------------------------------
            if(isset($label)){
                $output[$uid] = array(
                    'value' => $GLOBALS['LANG']->sL($label)
                );
            } else
                $output = false;
        } else {
            //Вытаскиваем все возможные значения
            foreach($TCA[$table]['columns'][$column]['config']['items'] as $key => $value){
                $label = $TCA[$table]['columns'][$column]['config']['items'][$key]['0'];
                $output[$TCA[$table]['columns'][$column]['config']['items'][$key]['1']] = array(
                    'value' => $GLOBALS['LANG']->sL($label)
                );
            }
            //----------------------------------------------------------------------------
        }
    } else
        $output = null;
    return $output;
}

Try following:

$GLOBALS['TSFE']->sL('LLL:EXT:your_ext/pi1/locallang.xml:tx_yourext_pi1.label', 'altIfLabelNotFound'),