In Magento 1.9, the "Sale" translation only occurs once, in
Mage_Paypal.csv ("Sales" is used much more often).
You can take advantage from this fact and create a new translation specific to the
Mage_Catalog module, which will be used in product lists (if this particular block is from a different module, change
Mage_Catalog accordingly below).
To do so, create a theme translation file
app/design/frontend/[package]/[theme]/locale/de_DE/translate.csv (if it does not exist yet) and add the following line:
The trailing space is important! Magento has a quirk in the translation system, that translations where the original string is equal to the translated string are completely ignored. This results in a fallback to the translation from
Mage_Paypal.csv just as before. Adding a space (or a non printable character if you prefer) will make the string different and it will actually be used.
More on the topic: https://magento.stackexchange.com/a/78483/243