using sass to generate RTL & LTR css files in Omega 4
I guess it depends on what you define as being convenient.

The SASS part is easy, since sass support is already setup in Omega. You just need to setup some sort of a sass structure to write the CSS.

To change the language settings, you'll want to invoke the template_preprocess_html() function to override the html that's rendered.
function template_preprocess_html