Krul revealed the existing squad have helped welcome the arrivals.
The Dutch star said: "Some of them don't really speak much English yet so we have to help them. That will take a few weeks but football language isn't that difficult. It's given everyone a massive lift.
"It gives extra competition for places, instead of taking things for granted. We'd been just happy to get 11 on the pitch and a bench. We've definitely got strength in depth now. I'm just impressed by the quality.
"It doesn't matter what country they come from."