That may be the way they do things over there but it's not how you have to do things. I would make sure you and your partner are on board with explaining to your 5 year old that your house has different rules and cussing is not encouraged and if done incessantly or even after being told no, there will be consequences. Explain why you don't allow it so they understand and be patient because sadly you are having to undo or correct something they are used to in another environment as being normal.
We definitely don’t encourage swearing with our children but I also don’t make a big deal about it. The bigger deal that is made and the more “forbidden” it is - the more it’s going to happen. I think this could actually work in everyone’s favor and ruin the novelty of swearing and decrease it. Maybe not. I don’t know the child but personally I don’t love swearing but we just ignore it.