Music during gameplay

[GoodCountry234]

If you ever downloaded the experimental COW 1914 Great War map, a soundtrack plays when your turn starts, but it's the same for every country. I want to insert specific music for each country you play.

Example: you are playing the Soviet Union on a WW2 map. I want the USSR anthem to play while you play. Battle hymn for the US, Rule Britannia for UK and so on.

How do I do this (for local same-pc game)?