Most useful depends.... English and Spanish are at the top of the list, but I’d put Arabic ahead of French, but that would depend on where you are at. If you are in East Africa then Swahili. If in West Africa, then French. North Africa Arabic. In India Hindi would get you around. Russia would get you around all of the Russias yes, but nowhere else
My list was with the assumption that english is your first language and you live in the USA.
English and Hindi are the official languages of India. English and Urdu are the official languages of Pakistan.