Copy the functions.php from app/code/core/Mage/Core/ to app/code/local/Mage/Core/
and change function __() function
from
function __(){
return Mage::app()->getTranslator()->translate(func_get_args());
}
to
if(!function_exists(‘__’)) { function __() { return Mage::app()->getTranslator()->translate(func_get_args()); } }