Best practise to build a two language website (with html)

I have a ready made html template: http://preview.themeforest.net/item/hostly-responsive-html5-template/full_screen_preview/18002354

I want to implement the language section (next to login). I want to build the website in english and greek language, when the user choose his language, the website should change the link to ….com/en or ..com/gr

What is the most efficient way to do that? Can i do that with javascript with an easy way using a plugin?