Rsync spends a lot of time (and bandwidth) backing up all the extraneous locales when a full system backup is performed.
It takes up a lot of disk space for features that will never be used on this system, which is based in the US.
Would it break Raspbian if all but the en directory were removed?
Turns out it is not a good idea to turn localpurge loose on a nicely-tuned system.
It is too unpredictable and yes it can break Raspbian. I had to re-image a SD card after running it, to start over.
Also, when using --delete and --delete-excluded options with rsync it minimizes the data transfers after the initial run.
So rsync basically has solved the problem after all was said and done.