The technical stuff is not as easy as you might think. Literally everything in a website needs to be flipped. This means that if you're writing your site code in vanilla CSS, things are going to get tedious very quickly. Throw javascript plugins into the mix and you've just signed yourself up for a whole new front-end project.

When I worked at ZURB, I was part of the team that brought RTL support out of the box to the Foundation framework. It would have been a nightmare to implement without Sass; we would have had to maintain two separate codebases. Instead we created a single variable that can be changed in the settings file that affects any horizontal direction in the project.

This changed the way the team wrote components. For example, instead of writing margin-left everyone had to switch to writing margin-#{$default-direction}. This prevents any hardcoded horizontal direction styles and sets the direction control in one place.

I think bootstrap has been working on a similar RTL implementation.

The idea is you would need to start with the code for either language, then change one variable to generate CSS for the other language/direction