We did an update on production but still a translation which was newly defined in a
translate.csv file did not work.
rm -rf var/cache it still was not shown. We verified that the folder is empty.
/tmp/magento also did not exist. After refreshing the page
var/cache got filled again - so it is in fact used.
We were able to make it work by
Flush Magento Cache in the backend - how can this be? Where else might the translation be cached?
We found this in the
<cache> <backend>apc</backend> <prefix>APC_</prefix> </cache>
The question is why Magento still writes to the cache folder.