Bug (?): Cannot read property 'ltr' of undefined

Hi,
I just updated my ckeditor with release 3.4.1 and I'm getting this error (in Chrome):

Uncaught TypeError: Cannot read property 'ltr' of undefined

In row 238 of file _source/plugins/bidi/plugin.js

addButtonCommand( 'BidiLtr', lang.ltr, 'bidiltr', bidiCommand( 'ltr' ) );

What is this plugin for?

HIH
~Aki