Do you still need paper boarding passes for international flights? Or are mobile passes fine?

I've not flown yet where I was not issued with a paper boarding pass on check-in. You then present this with your passport at the boarding gate.
Mobile/electronic booking confirms are accepted at check-in though.

If the airline offers mobile boarding passes, then obviously they accept them.
Note that a mobile boarding pass doesn't necessarily mean pulling up a PDF of one you are supposed to print.

Mobile passes are fine

You have selected a best answer, but I will answer anyways.

Paper or mobile is fine. Just make sure to present your phone with the proper bar or QR code on its display when requested.

Airline/airport dependent.