Birgitte SB wrote:
Then there are things like creating translation and adding value to text by wikilinks.
In my opinion, translations (performed by wiki volunteers) should belong in Wikibooks and not in Wikisource, exactly because they are not (pre-existing, external) sources but creative efforts.
Copyright legislation recognizes translators just like authors, so the copyright to a wiki-translation belongs to the translators, who can license their work. (I'm assuming that the original authors are long dead and no longer can make such claims.) Whereas most books on Wikisource are in the public domain, where none of the wiki volunteers can claim copyright and thus cannot add any free license.