It's a rather perverse word: [Nestbeschmutzer](https://de.wikipedia.org/wiki/Nestbeschmutzer) are not the actual people soiling the nest in question, they are the people who point out that the nest got soiled by others. Those others are now being angry that their shit got public, casting the nest in a negative light. In short: The usual blame-shifting reaction to a whistleblower or merely internal critic. OTOH, it's a very nice word: As soon as you hear someone calling someone else a nest soiler you know that, with overwhelming probability, the group/institution is a complete quagmire. I guess it *could* be argued that "whistleblower" is a direct translation, OTOH the connotation inherent in the word choice gets completely lost. Modern German also uses "whistleblower" as a literal import.