It was only this summer that wikisource.org was split into language subdomains like de.wikisource.org and en.wikisource.org, so it is understandable that pages in the new subdomains still have a low Google rank. However, this is the same for all languages, and doesn't explain the difference that I see between the German and the English language subdomain.
This is wrong; it is not the same for all languages. The English one is privileged because wikisource.org/wiki/Anything redirects you to it.
Therefore, from Google's point of view, de.wikisource.org is "new", but en.wikisource.org is just a new name of a site that is "old".
Hence, I'm not surprised that the Google spider gives more priority to de.wikisource.org. In fact, it may still have been in the process of spidering the site when you put the stuff up, and then the spider may have come across a link to it, while Google might be thinking that it has finished an indexing run of the English one, thus taking a break before giving it another go.
Timwi