Some of the other things that are now normally specified in the lang pack (e.g. how to combine firstname and lastname to give fullname) allow to to override them using $CFG. (But actually, that might just be a historic thing.)
In fact, we don't even need to provide a $CFG override. If you are stuck having to use the 'wrong' languages for your Moodle site; and you don't want to start work on a lang pack in your own language; but you do really want to fix the sort order in your UI; then you can just use the standard Language Customisation UI to change that langconfig string. Doing that is probably easier than going into your DB and changing the collation (on every table and column).
(Also, as it happens, I know you picked a bad example. My experience is that pt_br is one of the better named lang packs. Certainly they have translated some of my add-ons in the past.)
However, fundamentally, like you, I am a bad person to be considering this. Anything you can do to get input from Moodle site admins, or others, would be really great.