First of all thanks to Westeros' modders
I tried the 0.51 version and I find a bug about the sound; with the non-english verrsions of Medieval some faction crashed when you tried to select their armies or their agents; the solution it's very simple: go in Medieval file, Westeros, Data and delete Sounds' file entirely. You will never have problems with this bug...
I'm sorry for possible spelling or grammatical errors, I hope that this will be useful for you...