It does not translate with the application but with browsers settings, it doesn’t style or fit any design. It looks differently on different browsers and it is really hard to explain to stakeholders “this is from browser I don’t have control over it”.
It does suck, but I think not for the reasons you mention.
I truly believe a nicer API would motivate developers to use it, and if native validations satisfy the product requirement, their styling does become a lesser concern.
But surely styling is still important, but another great topic to write about is the fact that you actually can opt-in to showing native validity errors in a custom way!
And your application should be looking at ... the browser settings.
I could see a case, if a user decides to somehow make a single website use a different language than the others. I guess it would be a browser's job to have specific languages for specific websites.
It works for presenting or selecting initial language. Even that is debatable because some big players don't even care about that and present language based on location.
Explaining to people they should go and change their browser settings is major hassle.
Automatic language selection based on location is an anti-pattern. If I am traveling, I don't suddenly switch my brain to another language. Whoever writes websites like that doesn't properly think about it.
It does not translate with the application but with browsers settings, it doesn’t style or fit any design. It looks differently on different browsers and it is really hard to explain to stakeholders “this is from browser I don’t have control over it”.