to my best knowledge, joachim wagner has nothing to do with vgsf. (i could be wrong!) i guess vgsf forwarded your profile to this guy who shows interest in your application. if he wrote to you in german, it is with high chance that the program is going to be taught in german!
kakasasa, why dont you tell him (her) that you are still waiting for VGSF's decision for your admission. (then probably s/he could give you some insider information about your application (to VGSF).) do not reject him(her) in the first place unless you do really not want to do anything related to that program. you might ask him(her) to send you more information about the program (in english if feasible).
Vienna is a nice and small city,I've been exchanged there for a year, and if you really wanna work in Eu, then either German/French for you would be essential to master!
Actually,Viennese speak german and there is a great chance that u will get the Austrian professors with the foreign degrees to teach in English, so if u really decide go there, learn some german before you go, which will help you with daily life.
Wienwind, thanks for your input! I definitely believe Wien is a great place to be. For me, PhD in Finance is just a mean to land in a senior banking or fund job. If i can get a decent job in any major financial center in coming months, I will definitely take that instead of PhD (in Finance) without much hesitation. I really want to learn some German. I love German philosophy and fairy tale so much. But i have to say probably I am going to recieve the rejection letter from VGSF soon. Good Luck to those being admitted!