Spanish is a good choice. Impressive that you know Russian. Spanish is the second on the list of being most popular in terms of popularity (numbers of native speakers) next to Mandarin but the third language in terms of influence Sources: https://www.infoplease.com/ipa/A0775272.html https://list25.com/the-25-most-influe...-in-the-world/ You can not go wrong when you can communicate with loads of people that live in a lot of countries.