I suggest Javascript
Not to be confused with Java, JavaScript is primarily a client-side scripting language used for front-end development. JavaScript is compatible across all browsers and is used to create interactive web apps, often through libraries such as jQuery and front-end frameworks such as AngularJS, Ember.js, React, and more.
JavaScript can also be used as a server-side language through the Node.js platform. Two years ago, Node.js was still quite young, but its community has grown a lot since then, and you can now find many resources here. You can also build hybrid mobile apps with JavaScript through using frameworks such as phonegap, while Facebook’s React Native allows you to build native mobile apps with JavaScript.