But there are 1 billion who speak Mandarin better than you. I don't agree with learning a language because it's useful. Unless scholar or obsessed with a literature, not necessary to read great books either, some translations are good. Only reason to learn language: aesthetics
Everything is a trade-off. Latin & Ancient Greek are best for appreciating must-read literature to the full, but have limited everyday use.
When Jim Rogers (hedge fund manager, smart guy) was asked where the world was heading, he said "both my daughters speak fluent Mandarin".