At present, the libvirt.org website doesn't give any information for how translations are done, nor how people can contribute to them. This should be addressed by updating the website to include this information, so developers know the process, and so potential translators can get involved doing translations. As a data point for use while updating the website, the libvirt transifex URL is: https://translate.fedoraproject.org/projects/p/libvirt/
it's now: http://www.transifex.net/projects/p/libvirt/
And now it's https://fedora.transifex.com/projects/p/libvirt/
Changed again to https://fedora.zanata.org/project/view/libvirt
The new contribution page links to the translation service we use http://libvirt.org/contribute.html#skills