The "Add Item" button doesn't appear to work consistently (it worked for me only after I deleted another item in the locale file); also the translation appears to be discarded when a newly-added item is bounced back from the server. (After the bounce, it can be edited without problems.)
See http://forum.pkp.sfu.ca/t/translate-plugin-add-item-dont-work/31156.
The "Add Item" button doesn't appear to work consistently (it worked for me only after I deleted another item in the locale file); also the translation appears to be discarded when a newly-added item is bounced back from the server. (After the bounce, it can be edited without problems.)