This is the message we drum into our children at a very early age (along with don't smoke, wait for the green man & don't pick your nose).
And quite rightly too, stranger = danger (it even rhymes).
My daughter has picked me up on this a few times;
"who was that mommy?", after stopping to chat in a supermarket
"oh, no-one ", as in 'no-one that you know and to explain it to you would take too long and is quite unnecessary'
"but you say we shouldn't talk to strangers"
It's funny how a change of environment causes a change in behaviour. In England I would never dream of going up to strangers on the street or in the supermarket or in the coffee shop and starting up a conversation, it's just not what I do...shy and retiring me (unless there's a glass or 3 or wine involved that is) But here in Germany if I hear English being spoken I'm all over them like a rash (after first checking to make sure they look 'nice' and that they are speaking 'proper' English (i.e. that they're not gymnasium kids showing off their language skills - although this is unlikely given the inherrent laziness of such kids, and I speak from experience here).
Yesterday I accosted a couple outside of Aldi (narrow escape there, I was about to go in myself (looking for Portugese wine, honest guv) call me a snob, but I don't do Aldi, or Lidl (shudder) and certainly not Netto) I heard the guy saying something in English to his wife as I walked past and I turned back to talk to them, because you just don't hear English being spoken here (unless all us expats are out together, scaring the locals, that is) It turns out they're visiting their daughter who (as if by magic) appeared (clearly not keen to entrust her parents with supermarket shopping on their own). She lives in the next town along the river from here and seems keen to employ me on an adhoc basis as an English teacher to business people, I have her details here and everything, shall have to give her a call and set up a meeting to chat about the possibilities. I, in turn, recommended our favourite expat drinking hole, Lulu's, which she hadn't heard of, surprising really seeing as the martinis are to die for!
Today I was in Starbux and overheard English again, which is not as uncommon in the middle of Essen as it is in Kettwig, although still a rarity. I stopped myself going over though - a group of dull business types, bleurgh! Definately strangers. Jasmine would be proud of me.