Edit file index.php,
FIND this line :
$news .= "<b>".$image_row['news_title']."</b> -- Posté par <b>".$image_row['user_name']."</b> le <i>".format_date($config['date_format']." ".$config['time_format'], $image_row['news_date'])."</i>";
and REPLACE by this one :
$news .= "<b>".$image_row['news_title']."</b>".sprintf($lang['news_posted_by'], $news_row[$i]['user_name'], format_date($config['date_format']." ".$config['time_format'], $news_row[$i]['news_date']));