THE Scottish cast of the new Disney Pixar movie Brave, the forthcoming animated adventure fairytale set in a medieval Scotland, had to alter its script and insert real Scots words to make the film authentic.

At a press conference for Brave, which is to receive its international premiere in Edinburgh this month, its Scottish stars Kelly Macdonald, who plays the lead character Merida, and Kevin McKidd, who plays Lord MacGuffin and Young MacGuffin, said they had inserted words and phrases such as "manky", "gammy", "numpty", "hurdies", "quine" and even "Jings, crivvens, help ma boab" to make sure the spectacular film felt "right" to Scottish audiences.

Macdonald, from Glasgow, said: "They did an amazing job of writing a Scottish script in San Francisco, but there were certain things that just didn't ring true and I knew truth was important and so we felt comfortable saying 'that's not really a Scottish word' or there's other words that could substitute."

McKidd, originally from Elgin, added dialogue in Doric into the script for a comical character who is hard for the rest of the characters to understand.

He said: "It was great fun to play these characters. I rarely get asked to be Scottish anymore – I am usually doing cod-American accents.

"I was asked to play Young MacGuffin, and he was to have this very thick, incomprehensible Scottish accent and what I loved about collaborating was that instead of it being a generalised thick Scottish accent, that you couldn't understand, they were interested in my local accent – I was able to bring that to the party and I am very proud of that, that Pixar were willing. It was a lot of fun to speak in my crazy local dialect."

John Lasseter, chief creative officer at Pixar, said: "It was funny because we started getting notes from different people in Disney saying 'we don't understand these words, we should probably change it so that they are words that everyone can understand' and we were like 'no, we love that because we don't understand it, because we know that they are honest and true'.

"Part of it was that we wanted all the families and people going to see it in Scotland to look up and go 'wow, they captured Scotland' and it was really important to have these great actors to help us with that – and we really did tap into them, being raised in Scotland and bringing as much of true Scotland to the film."

Mark Andrews, the director, said: "We had 'hurdies' [buttocks], that came from Craig Ferguson [who plays Lord Macintosh], and Billy Connolly [King Fergus] had too many to mention, some of them not appropriate. We always had to check –'what does that mean?'"

The film, at the centre of a promotional push not only from Disney Pixar but VisitScotland, is the closing film of Edinburgh International Film Festival, on June 30, where it will have its first screening outside the US. It open in Scotland on August 3.