I forgot to mention that there are "maintainers" for each language too. This maintainer is not only a translator but also a leader and representative for the translators of a particular language, he collects po files from translators in the team and send them to the translation manager on a regular basis. IMO the translation manager doesn't have to be very dedicated, he just has to check the email everyday and time to commit po files. Atleast that's what The Battle for Wesnoth is doing now. Having said that, I agree that an online translation platform like transifex or launchpad is very handy,