This mod increases the soft cap on XP gained from Barbarians from 1 to 2 after the first promotion, and permits units to earn an additional promotion level before no longer gaining XP from Barbarians (3 instead of 2).
These values can be easily customized in the annotated TCS_More_Barbarian_XP.xml file located in Documents\My Games\Sid Meier's Civilization VI\Mods\TCS More Barbarian XP.
To install extract the contents of the zip file to Documents\My Games\Sid Meier's Civilization VI\Mods.
More Barbarian XP 1.0
Increases the cap on XP gained from Barbarians.