I dropped Spanish which was the only language offered during my high school years. I regret it, and now I'm embarrassed to start learning as a uni-aged guy. I want to learn Mandarin because then I would know English and Mandarin which would cover like 50% of the populations speaking abilities.
Basically I just feel like a dumb American and being a Marxist I need to know another language.
Well, nothing stops you from learning it now that you're uncomfortable with not knowing a secondary language. A different language is extremely useful when reading books from another country. It's a whole new universe you can discover if you're able to read and comprehend a secondary language.
In that respect, you should definitely plan before you begin learning a language. Think about why you're learning the language, and if the language is useful for a particular goal. You can be learning because you enjoy the challenge, etc. But it's a long-term commitment, you'll be learning that language for the rest of your life if you want to keep it.