I  am using a slightly different approach,  with the use of a skin helper to load a culture specific CSS file like the one on codeplex, http://stylehelper.codeplex.com/ although in my case my skin developer developed a skin object for that purpose.

The approach would be to have the skin.css load the common selectors and attributes for both languages and then load  specific css file for the  default language and another css file  for the RTL language (when one switch to the other language). Both use the same skin but with different css files specific to the language.

The two language css files are very similar except for the dir, float, left and right padding and margins and well as some align attributes, so customization is very simple.

Having one common skin is better for content translation as the secondary language will load the translated module in the exact pane of the default language plus maintaining one set of skins is easier, having the same feel and look .

In my case I kept the backend: edit, host, admin, module and page settings in the default language