English. Perhaps as your first language mandarin/ Spanish win but as the most known language even if used as a 2nd or 3rd language I’d go with English
China has the largest number of English speakers. I think we're done, China reminds me a lot of 40's-60's US in terms of "drive" towards education & industrialization. The US reminds me of mid-00's Greece.
Well I already speak English so focusing on Native spoken language. ANyone can get by in this world speaking in English as first and only language because so many others speak English. But the value of speaking a 2d and 3rd language has been priceless for me in terms of business development and socially as well.
I made my money with my Spanish ability and certainly helped in many wonderful social settings. There is an old joke: What do you call someone who speaks 2 languages..... bilingual What do you call someone who speaks 1 language.... American
I used an app called memrise which was like $30 per year. It has video of native chinese speakers saying words and sentences to help, but I agree...a private teacher would be better, unfortunately, my schedule is all over the place, so I can never have a set day/time to learn.