Well, not Esperanto. If you want to be successful in international trade, which languages should you speak? One answer is, the languages of those doing the trading.
Inspired by an article in the Economist, we quantified the native languages of international trade (exports and imports). That is, which languages are international executives most comfortable with (this differs from what is actually used). This should give an indication of which second language to study.
The language shares above are calculated by first quantifying total trade (exports plus imports) for each country in 2014. We then assigned a language to this trade volume (in the case of some multilingual countries, more than one language; the Scandinavian languages were combines because of their similarity).
For reference, Western European languages accounted for 67% of the total in 1974 — 56% of the total in 2014.