Download your languages files from the SVN repo...
I would strongly advise against this. The repo, as storage of language files, is being discontinued, in favor of Translate WordPress. Right now, you have no guarantees that the repo has a current version of the file.
The current method of getting language files is either to download (export) them directly from Translate WordPress individually (core, admin, network and themes). You can access that directly with something like:
http://translate.wordpress.org/projects/wp/dev/de/default/export-translations?format=mo (for the .mo, replace with format=po for the .po)
Above examples are for core files only, you'd need to repeat that for /wp/dev/admin/de/default, wp/dev/admin/network/de/default, and the themes.
You can "curl" all that, obviously.
We're aware that the method is a little convoluted at the moment, but we're working on a better export tool.