Cron job template block not being translated, but testObserver is

Question

I am configuring a product out of stock notification / alert, and I'm having an issue with localization / translation (pt_BR) in Magento CE 1.9.0.1.

The email/productalert/stock.phtml block isn't being translated when called by cron job. Nevertheless, when I call /productalert/add/testObserver it gets translated!

I am certain that when called by cron:

1. Module name is Mage_ProductAlert;
2. Mage::getStoreConfig('general/locale/code', Mage::app()->getStore()->getId()); equals pt_BR;
3. $locale = Mage::app()->getLocale()->getLocaleCode(); equals the same, pt_BR;

Any hints ? This is happening in core code, without any out of stock extensions.

Thanks!