Hello,
Currently epesi does not provide a way to backup the whole installation.
To perform a full system backup we usually resort to database backup (SQL dump) and backup of /data/ folder (that part is very important for several modules).
All translations are to be placed in /data/Base_Lang/ folder, with filename consisting of two letters symbolizing the translation and of course php extension (en.php - for english). This is where you can find existing translations and add new.
Hope this helps,
Arek