I'd guess Javascript is quite popular[0] because it's literally on every modern computer and has incredible reach[1]. It's also a bit of a kitchen-sink language so students can grow into a style and paradigm that suits them. Plus there's nothing to install to get started... just open a browser.

[0] http://www.tiobe.com/tiobe-index/javascript/ [1] https://tessel.io/ https://www.sitepoint.com/creating-webgl-game-unity-5-javasc... https://www.youtube.com/watch?v=5sETJs2_jwo