I had a same problem, so I found a line number 26 in plog-globals and there put my language like this: $locale = "cs"; You can try it, maybe it will work for you. Just try to put there it....
I did that and it does translate, BUT it returns these errors
Notice: Undefined property: gettext_reader::$ORIGINALS in /home2/mydomain/gallery/plog-includes/lib/gettext/gettext.php on line 83 Notice: Undefined property: gettext_reader::$TRANSLATIONS in /home2/mydomain/gallery/plog-includes/lib/gettext/gettext.php on line 94
In the plog-globals I changed (using trunk-589) line 38 from "en_US" to "it" and left line 46 "en_US"
If I change also line 46 to "it", it will go back to english.