>>3824011It's easiest to read another language, then write, then speak, then listen.
If you're a native english speaker, Spanish is incredibly useful in the US and will help net you a job, for example. If you intend to go for a more high-brow job then German or Mandarin would be useful. Spanish and German are fairly easy to learn.
Other options include Korean, (relatively easy to learn, good job opportunities) Japanese, (relatively difficult to learn, good job opportunities) Russian, (extremely easy to learn, so-so job opportunities,) and Arabic (moderate difficulty but good job opportunities.)
I'm not an expert in all of these languages, and feel free to investigate more, (like French, Hindi, Urdu, Portuguese, etc) and if so be sure to contact people who speak these languages as a second language for additional knowledge, but this should get you a general idea of usefulness, I think.
t. native english, secondary spanish, learning German and Russian