How to make unique "user interface" for each culture group
It's quite easy.
1. Unpack .pak files from your Data\packs folder using Vercingetorix's PAK Extractor.
2. Copy unpacked files into your Data directory or simply create here following folders:
3. Copy unpacked folder Data\UI\ROMAN\INTERFACE into each of these new directories.
4. Now you can begin to change files in INTERFACE folders to create unique "user interface" for each faction groups related to certain culture type.