This slip is from season 7, episode 151 called Farmer Buchman. I'm not completely sure.

In this episode Mabel finds a doll in the supermarket which is actually from a Dutch baby. They call the doll something like: Gerflunkenflunken. Since i'm from the Netherlands i know this doesn't sound like Dutch at all. Later in the episode you hear the father talk on the phone with the dutch mother Wilma, they use a make-believe which is nothing like dutch at all.

I find this pretty dumb. In a series like friends, for several episodes they took the effort to really use dutch sentences when needed.