Based on feedback received from many of the calibre translators, I have decided to move calibre translations from Launchpad to Transifex. Instructions for setting up a Transifex account and starting translations are here:
http://calibre-ebook.com/get-involved
All existing translations have been copied from Launchpad to Transifex.
Transifex has both a web based translation interface, that is much nicer than Launchpad, and you can also download/upload .po files if you prefer to work offline instead.
Please feel free to ask if you have any questions/concerns. This is my first experience with Transifex, so I will do my best to help, but...
The main problem with Launchpad that prompted this move was the frequent timeouts that occur in its web interface and also, in the last month, the updated translations are not always making it into the calibre releases because of launchpad server problems.