Im no SEO expert, but to promote this site further from a SEO pov you have to differ between Google DE/ENG and esp. ger/eng native speakers imho.
German users will mostly have Google set up for DE results, english for ENG. So german native speakers will likely get much worse rank for SE than eng., as it is more unknown there (look at the regions) and there is heavy competition with german language forums. There are not many german programmers coming from other SE sites probably with high interest in german language questions...Improving the rank of Google DE results looks pretty tricky to me.
Do you want to promote this site on english speakers AND/OR germans? SE seems to be much more popular in ENG web then GER.
I saw here some asking questions in German, i think thats ok, but maybe in the BETA stadium it would be better to ask questions only in english? But im not sure about this. English guys starting to learn German might feel a bit lost and intimidated to ask "stupid/very simple" questions, but thats imo the way to make the audience grow here in BETA. Of course you need good native speakers here who give high quality answers, but imo germans are not the main audience, as hard to recruit and there are enough german forums.
Concerning english users i would promote this site in eng. philosophy forums. There probably often german language questions arise and these forums are good frequented.
I think some SE sites have the fundamental problem that they run out of good questions as the topics are not evolving in time unlike e.g. physics or programming knowledge & technology.
Is there a threat concerning the site launching process on SE, that this site will get closed? Or does a site just have to survice the BETA, can someone give a link plz. explaining the launching process?