I could be wrong, but maybe the problem is that there is no international equivalent of the custom replacement above.
The closest thing I could find is this, and I'm at a loss to understand what this even does.
Code:
if (isset($this->transittime[$service]) && $this->transittime[$service] == '' && preg_match('#(GXG|International)#i' , $service)) {
$time = $Package['SvcCommitments'];
$time = preg_replace('/Weeks$/', MODULE_SHIPPING_USPS_TEXT_WEEKS, $time);
$time = preg_replace('/Days$/', MODULE_SHIPPING_USPS_TEXT_DAYS, $time);
$time = preg_replace('/Day$/', MODULE_SHIPPING_USPS_TEXT_DAY, $time);
$this->transittime[$service] = $time == '' ? '' : ' (' . $time . ')';
}