Mod\modname1\localisation folder
From EU3 Wiki
The localisation folder contains files that define all of the names of governments, countries, event titles, event descriptions, and other text for a mod. There should not be any subfolders in this folder as of patch 1.1. Any .csv file that has the same name as a file in the EU3\localisation folder and is in this mod\modname1\localisation folder will be used instead of the .csv file that is in EU3\localisation (the original files will not be changed even if they are named the same). The code that is used in the mod\modname1.mod file determines how the event files in this directory are used. please see the description of that file to learn what codes can be used and how they work. As an example, we will use .csv files with the same name as some in the original game and some new ones. Mods can use any name here for .csv files. Only .csv files are looked for here by the game. Modders can add thier own code into a file such as text.csv but if the modder is only adding code and not changing original code, it would be better to make a new file. As an example, modname1.csv is a newly created file where as text.csv is a original file that this example mod is going to change. When adding or changing mod content, you usualy need to add or edit .csv data. Changing or adding event files do not require .csv file changes/addition unless you want to use titles and descriptions from a .csv file. As an example, if you just type in the title and description like this: title = "myeventtitle" desc = "myeventdescription" in a event instead of using the code like this: title = "EVTNAME5001" desc = "EVTDESC5001" then you do not need to worry about .csv files.
