What is the soundest way to adapt an HTML application to an RTL locale?

What is the soundest way to adapt an HTML application to an RTL locale?

1. Update lang and dir together, use logical CSS properties, isolate unknown-direction fragments, and review icon semantics.
2. Set text-align to right on the body and leave the rest unchanged.
3. Apply scaleX(-1) to the entire application.
4. Insert direction-control characters into every translated string.