Is there a bookcrossing app
I downloaded one but it seems to be in Russian. And something about a qrs code.
There is no official BookCrossing app that currently exists. Therefore if you have downloaded something, it is not affiliated with the BookCrossing site.
What has recently been introduced by us, are QR codes on BC Bookplates, however you do not need an app for this. Scanning the QR code can be done simply using your smartphone's camera, and ours land you on the 'Make a journal entry' page' for that specific book.
You can read more on this here: https://www.bookcrossing.com/---/770