I never read Kehaar as stupid as such, the black headed gull proved very useful. I'm not sure what the accent was meant to be (it was bloody hard to read), but as Adams based him on a Norwegian resistance fighter from WW II, it was probably an attempt at some sort of Scandinavian accent. I wondered why the field mice spoke with exaggerated Italian accents (they may not in the film, but they certainly did in the book).