"What are you talking about?"
Translation:Hvad snakker du om?
I don't think "pratar" is a word in Danish, but the impression I've always got is "at tale" is a little more serious and formal, whereas "at snakke" is a little more casual, but generally speaking they are reasonably interchangeable (but any native speakers, feel free to correct me)
I concur. I'm no linguist (however I am a native speaker). In a formal setting I would use 'tale', whereas 'snakke' is used in more verbal and/or familiar settings. You would 'tale' with the Primeminister. 'Tale' or 'snakke' with your grandparents; and 'snakke' with your friends.
I'm thinking a great way to differentiate is to think about the french use of 'tu'/'vous'