There are three letter language codes, e.g. fur.

So there's no chance it will try to use the Torified DNS server, in
case our firewall fails.

It makes a bit of sense on its own, and it guarantees that no weird
cruft in ~/.tor-browser will interfere for whatever reason.

No code is deleted/added/modified, only moved.

This way the chroot browsers will close faster.

We could use `cp --no-dereference` before, when the TBB_EXT dir only
contained symlinks. This will reduce the memory footprint of the
chroot browsers, and incidentally fixed a bug where the
unsafe-browser's name wasn't set since we copied the langpack before
we fix the name in it.