I don't know anything for certain since I am just a player of this mod who enjoys it very much btw.
I noticed some different spawning points in scenes compared to the previous version. I also didn't encounter any scenes bugs so far in sieges or on prison break-out missions
I also get skript error messages very seldomly now while they were very prominent in 1.11.
Also my troop names are all Latin like I selected in the installer.
All in all, 1.13 seems to have done some polishing and fixing small bugs.
P.S.: If anyone knows how to make the world map a bit brighter, you must post ITT.
Edit: Just noticed I can't see my Right to rule stat on my character report. Anyone know what's up with that?