Indeed, the issue is related with the use of special characters in two files. Please do the following:
Rename the files named "WSS_Lully_La_Marche_Française" as "WSS_Lully_La_Marche_Francaise" and "WSS_Lully_Marche_du_régiment_de_Turenne" as "WSS_Lully_Marche_du_regiment_de_Turenne". These can be found in your game installation folder at: ...\Wars of Succession\WSS\Sounds
Then download the file attached in this message, unzip it and replace the "Music.ini" file in the "Sounds" folder with the extracted one.