There's various places in Moodle where Right-to-left text systems are catered for.
Moodle also has a fairly sophisticated system for building up the various CSS files necessary for different themes, modules etc. and outputting a single CSS file containing all appropriate CSS.
It might be a good idea if the various bits of RTL related CSS that are currently contained in multiple files were moved to a single rtl.css file (or multiple such files, one for core Moodle and one in each optional module etc.).
As well as possibly making it easier for people to work on these areas, and allow the CSS to be simplified and condensed across Moodleit would also be possible for a Moodle system to know when rtl.css is not necessary (as no language that requires it is being used) and simply not include the rtl.css in the output to allow for faster download and display of the page in those cases.