That make sense. So please consider this a feature request, as opposed to a bug report.
Using ASCII is fine for now, there are few french-speaking websites using IDN.
But there probably many arab/chineese/russian-speaking websites that do, so it may be more annoying for those users.
N.B. I’ve sent a flattr micro-donation as a gesture of support
@rfc2822 ideally it would be used by all apps that use Nextcloud login but it currently has shortcomings which can only be addressed by further work on how the server (Nc) handles app tokens.
One would say the most important thing is push, but that takes along quite a lot of things with it - ATM that means remote wipe for example and potentially other things in the future. Like I said above, this will hopefully be addressed in one of the future versions of Nextcloud.
I’d also say UX is currently better when you just do the auth screen on your side, but that’s a matter of opinions as both ways have their pros’ and cons’.