Re. German - my native language is portuguese, I also speak and write fluently in english, french and spanish and manage to keep a conversation in italian and german. Therefore I will keep myself away from this debate, since I am all for language diversity. Languages are beautiful.
But I always found it easy to grasp both a language and pronunciation. German is quite easy in terms of getting a good accent, for me the problem is, in order to speak it correctly, first you must build the whole sentence in order to get it right, unlike the other languages I speak. Therefore writing in german is no big issue, yet speaking it is quite hard for me.
I guess this is all about where you live and how much you practice it. If I lived in a german speaking country I would learn it quickly. And one could say that about any other language, I guess.
At the end of the day, I believe a simpler language, in which you can get understood even when your accent is not that good or you make some grammatical errors, and that lots of people talk frequently (or listen to) will "win" in the end.
Numbers in media content - movies, tv, music, internet - will be the key. The sound of it will have to be the most familiar to us all.