Those are notices, not errors. We're working on eliminating them, but for now it's ok to just disable the display of notices. In plog-globals.php change line 10 from
<blockquote>error_reporting(E_ALL);</blockquote> to
Are you sure you installed the r556 files? PATH_TRANSLATED is no longer in the codebase (it uses SCRIPT_FILENAME now instead and most, if not all, the notices should be cleaned up in 556).
Also, I would recommend downloading and installing r549 if you are just trying to get translations to work. r550 changed the structure of Plogger and may cause some issues during upgrade.