They're culture based, although some cultures may share the same voices, so if you want them separate, you have to divide them.

For instance, if it says:
culture roman, greek
then the voice list is shared by romans and greeks. If you want the greeks to have a different one, you have to move it to another list or copy and paste an entire list and put the greeks there.

Unless the Latin voice pack replaces the entire sound pack files (I doubt they did), then putting in vanilla sound text files should revert you back to vanilla voices.