There is a folder called /localisation that contains a whole bunch of .csv files that contain all the text localisations for all the variables used in the game. In most cases the text is a single entry with interpretations for English, French, German and Spanish, but sometimes the text has multiple entries depending upon the culture or religion of the target.
For example, the localisation for Court Poet reads -
title_court_poet;Court Poet;Poète;Hofdichter;;Poeta de la corte;;;;;;;;;x;
The localization for Count however depends upon the culture of the target, here are a few entries -
count;Count;Comte;Graf;;Conde;;;;;;;;;x
count_saxon;Earl;Graf;Graf;;Conde;;;;;;;;;x
count_english;Earl;Comte;Graf;;Conde;;;;;;;;;x
count_scottish;Earl;Earl;Graf;;Conde;;;;;;;;;x
count_irish;Earl;Earl;Graf;;Conde;;;;;;;;;x
If you want to add your own localisations for various titles all you have to do is edit that file to add your localization, eg -
count_russian;Graf;Graf;Graf;;Graf;;;;;;;;;x
Far better is to create your own micro mod that overwrites the default values when the game is fired up. Easy to do, it means that the vanilla files are untouched, and your changes won't disappear every time a patch is released.
The modding forum has more info, otherwise pm me for details.
Cheers