While fixing #5967 I noticed a few things.
1. We use U.S., which is a bit old-fashioned. "US" would probably be better (also recommendation of style guides like for The Economist.) Same for U.K.
2. We have the following in the en locale, which is not very consistent for the US and UK:
The format of this listing is long/short combined, then long/short uncombined
I think the following would be better:
That would involved adding alt="short" values for "en_GB", and "en_US".