Registration is not working for English users (when you're doing it with https://wowcircle.com/en/reg.html) but it's working with Russian version (https://wowcircle.com/reg.html). When you choose a realm it leads you to:
This page isn’t working
wowcircle.com is currently unable to handle this request.
HTTP ERROR 500
I don't know where could I put this report so I hope I didn't violated any of the rules. I think it needs to be fixed because I guess majority of potential and possible english speaking players would be rejected by this kind of bug. As for me it's not a problem since I can understand some of the Russian language (because of cyrillic script being my maternal one), but it can be a problem for others.
Best wishes to WoW Circle staff! ♥