Facepalm

Not sure anyone will find this interesting in the slightest, but in Steam as a developer you configure your game as multiple packages they call Depots. You'd have a base package everyone gets, and then other packages which download on top of that for variations. Language is one of the possible variations, and whoever configured steam for Fallout 3 kindly separated them out, presumably because the audio files are quite large and most players will only ever hear one set of them.

Regional differences are also handled this way, often something like a blood texture will be modified for certain regions, and there may also be a Germany specific depot with Nazi symbols modified. Depending on your Steam settings, and where you are in the world, you end up downloading some combination of depots that combine to make one out of potentially dozens of variations of that game.

I don't know if the Xbox app provides the same functionality, but if so it would be a completely different implementation from Steam and the person who set it up either couldn't or couldn't be bothered.

The Steamworks documentation is public for anyone who likes that sort of thing: https://partner.steamgames.com/doc/store/application/depots