This. Ftfy has saved my as many many times. Thanks for the regex. brilliant.
A developer upstream naively split on /n and leave some errant /r characters everywhere? Fixed.
Embedded backspaces or nulls or tabs or any sort of control character? Gone.
Non-ASCII data in a field you know should be ASCII only? Ha, not today good sir!
Until you've had to deal with the hell that is raw, free form data from who-knows-where, you cannot even fathom how satisfying it is to be able to deploy that regex (when appropriate) and know beyond a doubt that you can't have any more gremlins hiding in that particular field/data that'll hit you later.
In Portuguese, which I’ve worked with, you develop other tricks, like replacing à, á, â or ã with a. But, in order to do this, you still need to find out the encoding used before you can create the “ASCII” equivalent.
Fun trivia: coco means coconut; cocô means poo. So, by replacing ô with o, you’re guaranteed a chuckle at some stage.
Never did I see the parent mention "this is sufficient for humans", or just "...for English" - even that would be a naïve assumption (see? ;)).
I would rather pass around a link to https://ja.wikipedia.org/wiki/メインページ than to https://ja.wikipedia.org/wiki/%E3%83%A1%E3%82%A4%E3%83%B3%E3... , and lots of software will support both. And if you want all URLs to be ASCII, you'll need to convert the first into the second, not just delete the Japanese characters.
In user interaction with a browser or wherever else it seems that anything goes.
It's true that protocols such as HTTP only use ASCII URIs on the wire. If you are implementing an HTTP client yourself, you will need to implement percent-encoding.
Which is different from saying "well, I know URLs should be ASCII on the wire, so I can safely delete all the non-ASCII characters from a URL." That's not true.