Hugh (Dr. House) Laurie, appearing on The Graham Norton Show (Series 9 Episode 4) explains that in Germany, the word (or sound) for ‘Boooo’ is, instead ‘Ooooh’. [from 1:00 onwards]
The incident is backed up by academic research :
“Until the nineteenth-century, there is no evidence of booing: hissing and whistling are generally preferred. Booing is now widespread in Britain and the United States, but less common elsewhere.”
Dan Rebellato, who is professor of Contemporary Theatre and Head of Department at Royal Holloway, University of London, (and who is an associate editor of Contemporary Theatre Review) explains in a paper for Contemporary Theatre Review, Volume 23, Issue 1, 2013, entitled, simply : ‘Booing’
The full text may be found here :