If the same culture, unlikely to be compatible--the one loaded last will overwrite the other. You will need to cut the relevant code from one of the mods, and paste it into the mod you will actually use.

Is the mod compatible with other mod that make changes to the affected culture?

still compatible. affected cultures were not updated in 1.6

added Welsh, Pictish and Breton

give me a minute, will add. Had to get it to work first.

I have been looking for this. Is it not also possible to have it also fo Welsh, Pictish and Breton ? Ladies used to rule Celtic Gallia and Britannia