在php中的setlocale（），ç在日期名称中不起作用，如terça-feira，只是显示�

Yes, I've already changed the charset a lot of times. If I set the charset to ISO-8859 it shows ç but the accents doesn't and if I change the charset to UTF-8 the ç which is generated turns into � but the accents are showed. Here is the code

<?php
    header("Content-Type: text/html; charset=UTF-8");
    setlocale(LC_ALL, "ptb");
    echo "Dia da semana: ".strftime("%A", time());
?>