Be sure to visit the Trace Modeler website for updates and UML sequence diagram resources!
Trace Modeler fully supports bi-directional (bidi) text, i.e. left-to-right and right-to-left scripts.
I've tried to support right-to-left scripts as much as I can, but my infrastructure and experience with it is limited. If you find anything missing/wrong or have ideas to further improve Trace Modeler for users with a right-to-left script, please contact me.