German is always useful... It's not THAT close to English, but it's part of the same family. Have a look at the link here: https://en.wikipedia.org/wiki/Germanic_languages However, it depends a lot on what your goals are and/or where you are trying to go or do....what your passions are. Once you take into consideration all that, maybe it'll be easier to pick your next linguistic challenge!

German. I think English and German are very similar Wir waren in Berlin. We were in Berlin.

Spanish. There are a lot of cognates from English and besides, it's just so cool.