This is an excerpt from Metamorphosis by Franz Kafka:
Just as he was thinking all this over at top speed, without being able to decide to get out of bed--the alarm clock had just struck a quarter to seven--he heard a cautious knocking at the door next to the head of his bed. "Gregor," someone called--it was his mother--"it's a quarter to seven. Didn't you want to catch the train?" What a soft voice! Gregor was shocked to hear his own voice answering, unmistakably his own voice, true, but in which, as if from below, an insistent distressed chirping intruded, which left the clarity of his words intact only for a moment really, before so badly garbling them as they carried that no one could be sure if he had heard right.
I noticed that there aren't quotation marks for What a soft voice!. I have checked other translations, all of which use the same technique. Is there any reason for this?
Stanley Corngold who uses quotation marks for all dialogues including thoughts does not use them either.