The duo - who have both won the Champions League - have already notched up 26 goals between them this season despite this being their first together at Rovers.
South African McCarthy speaks the language well after his time in La Liga with Celta Vigo, while Paraguayan Santa Cruz naturally speaks Spanish as his mother tongue.
“Roque and I are good friends and we understand each other,’ McCarthy told Goal.com.
“We always speak Spanish with each other, which confuses a lot of defenders in the league. They don’t have a clue what we’re talking about or what we’re saying, which helps. I think that we’ve done really well for two players from totally different backgrounds who are thrown in together.”
Nevertheless, after the stunning impact he made at Ewood Park last season, the Bafana Bafana admits he’s found things a little tougher in England this time around, where he’s scored only 11 goals.
“To be a striker in the Blackburn side now, it’s a living hell,” he commented. “Sometimes I get nightmares because I’m thinking ‘how can I go from being the second top scorer in the league last season to playing only whenever it’s my turn to play’.
“You get sleepless nights because of it sometimes but it’s just how the competition is in the team. I’m not having the greatest of seasons, I would have loved to have had the same season I had last year, but unfortunately they know all about the showboating now!”
And the South African admits that he has a friendly rivalry going on with the former Bayern Munich goalscorer to see who can score the most goals for the club this season.
“I’m not far off him,’ said McCarthy of the 15-goal Paraguayan.
“There’s not an official competition to see who can score the most but I think deep down you have that little competition. We’re the best of mates and we’re trying to do the best for the team. That’s healthy.”
The striker also revealed the ambitions of the whole side, who are aiming not just for Europe but to grab the final Champions League spot.
“At the moment people might say it’s an impossible dream but we believe we have every capability of reaching that fourth place,” said McCarthy. “We’ve got do-able games coming up. I don’t see any team in the next six games we’re playing that will be able to stop us.”