I'm impressed by anyone who can speak that many local dialects of English alone!

One of those 'undefined's appears to be en-us, which is strange...

I don't think so: en-us is right at the top, outside the main vaguely-alphabetical ordering.

Bah. I'd checked at the beginning of the list of ens for it, but not of the whole list.

The rest of the list appears to be in alphabetical-by-language-name (based on noticing cy (welsh) near the end).

The second undefined is where you might expect en-us to be, the first is where en ought to be; shunting them to the start of the list appears to have left holes. Anti-languages, anyone?