Robert has of course the option to use for his translation tutorial only those Wikipedia texts that have been released into the public domain,
Are there any? I know that you release all of your contris into the public domain, but once someone else starts working on them, they become FDL licensed.
The specific parts contributed by authors who release their work to the PD still are, and always will be, PD. Additions made by others are, as you say, under the FDL by default. But there are still some pretty significant chunks of PD text in the wiki, notably mine.