<p>From what I’ve heard and read, the Middle East and Russia/Former East-bloc are going to be the next big countries of expansion. There’s tons of people who speak Chinese/English, Japanese/English, Spanish/English, or Hindi/English, fewer speak Russian/English, Arabic/English, or Farsi/English. So of your list I’d say Russian or Arabic. </p>
<p>By the way, it probably depends on what you want to study, but I don’t know exactly what language is better for what fields of study.</p>
<p>People don’t speak Sanskrit, it’s studied like Latin or Classical Greek. It’s not marketable at all.</p>