Updated the mod, now it supports all others languages (That Ck3 Supports), if you found any error in the translation, please let me know about it. And i update the message that was show when you had too many duchies to show the correctly message

Hum, strange try a game in the debug mode with only this mod, and form four duchies and verify if it happens

I have 3 mods that edit MAX_DUCHIES_BEFORE_PENALTY, they are Rebalance+, Realistic Diplomacy Range, and this mod. This mod is listed below them in my load order so is overwriting them.

Searched contents of all mods, prior to posting that comment, also moved this mod to the bottom of my load order. And when I have 3 duchies get a -15 opinion. I had also started a new playthrough to ensure wasn't 'baked' into the save file

Skelly1983 for what i tried here its working fine, verify if no another mod is change this value here:
MAX_DUCHIES_BEFORE_PENALTY = 4

Opinion modifier "Too many dutchies: -30" still shows on my vassals when I have only 4 dutchies, even though no notification shows for it.

A suggestion, is it possible to make one for 5 duchies, since this would allow us to hold all 5 holy sites of our religions without penalties.