> Is there not an existing more browser-specific appropriate place for this to go?

Not that I know of.  The modern (aka AMD) way to get the locale is `require("dojo/_base/config").locale`, so it needs to be defined in `_base/config` or something `_base/config` pulls in.  There's no configBrowser.js file.

> The actual fix for #16663 is to make sure that targetLocale is an empty string instead of undefined.

OK, I'll make `require("dojo/_base/config").locale` default to "" instead of undefined.