OK, the translation of the 4.5.5 is ready.
Zimbra has kindly contributed with their own revision (d3vil's work in the SVN), and after some merging here we have the 4.5.5_GA_838.
As usual, the tar file with the date zimlet, the spelling patch and the installation script can be downloaded from http://files.whitehatmail.fr. Otherwise, here are the properties files. The same files have been uploaded to the SVN repository.