Can I ask what this literally translates into word-for-word? I'm curious :)
"What is it for fault", but "vad för" taken together often means "what", adding the idea "what kind of", "what sort of". det is a formal subject, like in It rains.
Yes, it's just that vad är det för fel is a very idiomatic way of saying it in Swedish.
Is it common to completely drop the -d in Vad the way the full-speed TTS does in this example?
Could you say "vad är det för en fel" and would the meaning change? I think this "vad är det för en" structure compares the object of speaking, case-in-point to the wider class of such things, suggesting this particular object is somehow different?
It is "ett fel", but yes you can say that, with a little different meaning. It is more like asking what kind of error it is. It could also be a rethorical question pointing out a strange or stupid error.