I've noticed that left and right in css templates are automatically replaced once you change to RTL language.
For example, float: right; is automatically replaced with float: left;
I asked earlier in the Styling forum if there is a way to stop this behavior for specific rules.
For instance, an element that will float to the left, both in RTL and LTR, and won't change into float:right;
The only answer I got is to use different themes, but this is not practical.