Well, if you ignore general trends and the availability of people for a specific stack, I suppose you could go ahead and write your app in a language like Haske

Well, if you ignore general trends and the availability of people for a specific stack, I suppose you could go ahead and write your app in a language like Haskell, or even languages like Rust. But if you want to choose a language that is "meant" for the web and it's something everybody knows, I'd blindly pick Javascript if I were you. Of course, it's not the best language for mobile, but frameworks like Ionic are changing that.