Book translation is done using the Transifex service. The project is located at https://www.transifex.com/qmlbookorg/qmlbookorg/dashboard/.
Please request for contribution and which language you would like to contribute. Translation is done by a community of people, so everyone can start translation a language. Only when the language is at least 80% translated it will be published.
Discussion is onging on the gitter account: http://gitter.im/qmlbook/qmlbook.
Please read https://docs.transifex.com/integrations/sphinx-doc and http://www.sphinx-doc.org/en/master/intl.html before contributing for translation.
To build your own translated version you need to pull your language and build the documentation with the correct language settings for German (de) this process would be:
tx pull -l de
make -e SPHINXOPTS="-D language='de'" html
And then you can load the HTML pages from _buld/html.
Note: This feature is rather new with the qmlbook so there will be questions :-)
/ jryannel