@btn: if you upload an xpi file all the locales are reset (they are replaced by the files included in the uploaded xpi) so that all modifications done in the translations are lost. For this reason you should collect the locale files available in WTS before uploading and include them in the xpi.
@markh: when you modify your locale it is a good idea saving it in order to have a backup copy in your PC (it is only a click in "Save locale as tar gz file.."). If something weird happens -a new extension upload, some problem in WTS, or any other issue you can imagine - you only have to upload the files.
Anyway, send a message to Fenian asking him if it is possible to restore your locale to its status before the upload.
I'm really sorry for this. I'm totally unaware of these kinds of stuff when I upload something new. For this last update, all I'm adding is just a string for the extension description, that's it nothing more. Next time, I think I should just post the string here and you guys can just send me an email with the translated string. This probably save both of us a hassle.