Magento 1.9 – Add Translation File to Custom Theme

If you set the options via the admin config section Customer Configuration->Name and Address Options then you can set-up each site with different values.

Otherwise by default the block used to translate will belong to Mage_Customer. See template /app/design/frontend/base/default/template/customer/widget/name.phtml.

Since these options are set-up via the admin section there is no "default" translations. You could do one of the following options. I think 1 is the easiest, 2 is the one you should not do and 3 is a good option.

1. Add them to your translate.csv file,
2. Add them to Mage_Customer.csv file (please do not do this as these changes will be lost if you update),
3. Create a custom module that deals with customer translations and put them in it's translation file,