Unfortunately, the access to VCS is a preferred method used by transifex.net (note that now transifex allows to pull .po files from .tar.gz and then the final translations are send by e-mail (!) to the package maintainer).
So... I started to use translationproject.org 3 years ago. And it works. It works very successfully without any automatic interaction with upstream VCS. The final translated .po files are available by HTTP or RSYNC. For example:
rsync -Lrtvz rsync://translationproject.org/tp/latest/$PROJECT/$LANG.po podownloads selected .po file to the po/ directory. I usually sync my private GIT repository with the latest PO stuff from translationproject.org few hours before package release. The next step after .po files download is to call git-add (for new .po files) and git-commit. The ideal solution is to commit with the --author= option where the author name is a "Last-Translator" from PO file.
Because I'm lazy, I have a script for this task:
git-tp-sync <project-name> [<lang> ...]And here is an example from git-log:
Author: Clytie Siddall
Date: Mon Mar 22 09:36:51 2010 +0100
po: update vi.po (from translationproject.org)