Best language for an International Relations/ Econ major??

Hence my use of the qualifier “unlikely.” While we will all know students for whom language study is a breeze, we do not know the OP’s capabilities. Regardless, the OP did not express an interest in either Chinese or Arabic, so the discussion is moot.

You can do business in any German-speaking country, such few as there are, without speaking German, English will get you by just fine.

French does get you access to Francophone Africa, but that isn’t such a major economic or political zone. Anyway, as a Spanish speaker, you can easily learn French on your own later if interested.

Russian is bit harder, so learning it in a structured way through university is helpful. Russian is spoken in a lot of countries, most of them where relatively few people even at the top are proficient in English. Russia and its language empire is large, and strategically and economically important.

So I think Russian is the best choice …

a U.S. friend of mine worked for Deutsche bank, he came from German parents, so had an easy time brushing up on German; but then they shipped him to branch in Tokyo so he had to learn Japanese! Funny.