[everyone's typing boldly now...]
Germany's officials are already complaining about the diminishing immigration. They also have the problem of "wrong" immigration, that is, illiterate and culturally challenged migrants who only want to keep the profile low while enjoying the German state benefits for the poor. Germany wants to attract the "better" migrants, but there are so many obstacles and minefields on the way to an immigration country that I don't think it will ever work out.
Think of it. want to go to Germany? Well, hmm. Speak German? No? Yes? You are fluent with an accent? Forget it. People with a foreign accent are labeled idiots in Germany. This is likely to kill Germany in the long run.
America, on the contrary, has a growing population that (mostly) speak English. It might sound stupid, but it is a huge advantage. No, not Mandarin or anything else. People around the world learn English, and it is easier to achieve an acceptable level compared to German (or, even more funny, Dutch or - much worse - Mandarin). That is a little but very important advantage that might save Americas butt.