Well, I can take most sound files and run them through a converter, then use split gvr to get them into CFS2. The problem is two-fold. First, they do have to be of the same size or smaller than the original. Second, you can only replace files that are already in the sim and not add new ones. That means we could create a collection of files that replace the stock ones. Thus turning an English sim into, say, a Russian one. But I don't know how to create a set that is strictly add-on.
I suppose I could try replacing all the old files (lets say, the English ones for example)with Russian and then take them out of the sim and rename them. However, I do not know if there is a way to to activate them in a country cfg. file if they were added back into a sim as a Russian language radio pack. Any ideas?