What's the difference between praten and spreken?
My guess is pretty much like the difference between "talking" and "speaking" in English.
That's correct, and according to Wiktionary, praten is related to the English words prate and prattle.
Is 'chat' an inappropriate translation of 'praten'?
Not necessarily, but I think 'to talk' is the most fitting translation. Other verbs such as 'kletsen' or 'babbelen' are more like 'to chat'.
I tried it with 'chat' and it was accepted.