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.

Unless you're making the backend/app to learn stuff, a very upfront benefit of using an "obvious language" is that it will be easier for you to extend the team in the future.

"Web/mobile app" doesn't give us or even you very much to go on in the decision. Pick the right tool for the job - or describe the job, and maybe we can help you out.

That this guy said,

You need to describe what you want to do, going to need to have video uploads and playback? Want to create something via some web GUI interface? Want to manage picture collections? Collect data in the field for orders to be uploaded later on? etc. All of that sounds easy to say but can have a boatload of complexity behind it. Some tasks can be easier on specific languages/platforms than others.

Javascript/Meteor