I am confronted with this centuries old issue in Swing and RTL languages. Whenever it comes to show Hebrew text in Swing components of any kind, the application just melts the CPU by font metrics calculations. I see the issue mentioned a decade ago, then it popped up in Oracle and recently in Open JDK bug repositories. People are even trying to hack the JRE by replacing the implementations with instrumentation tools.
This is an extremely old issue and it's unbelievable that it manifests itself in Java 8,9,10,11 and 12. Actually starting from Java 9 and up the usage of HTML with RTL in Swing components brings its rendering to a screeching halt making the entire app useless.
If anybody knows how to deal with this, please do share.