I have always had the opinion that you should learn what ever makes you happy. Watch my video above. I found a website that has a great little test which should help you figure out what works best for you.
Mastering a third or forth language is never a bad idea.The United States is a vast, self-contained nation, in which it is very rarely essential to know a language that isn't English. In a Global Economy, this is changing. Speaking Chinese is a great advantage when you need to purchase from Chinese suppliers. Have you ever uses Alibaba to purchase goods for your company? If so, you know the importance of knowing Chinese.
Did you know 100 million people speak German?
Why learn Polish? Polish language learning sites are few and far between.
Learn what ever makes you happy.