Words/phrases/idioms which don't exist in the putative language

I was surprised when a London camera store clerk said “cheerio!” as I was about to leave (no “pip, pip,” though).

I’m not sure what you mean here.

Stein, used in English, I’ve only heard in names (usually to sound stereotypically Jewish - stereotypical non-Jewish German names usually get a ‘von’ or ‘mann’ in there.), or as a kind of beer mug, which is called a stein, in English.

I’ve never seen it in the same sense as ‘sacre bleu’ or ‘ah so’, or to give a more common German example ‘schweinehund’.

I have an Italian cousin (by marriage) who says “ooh la la” as his primary exclamation of surprise/excitement/whatever.

In the war comics of my youth when our honest ,clean cut Tommies were giving the fiendish storm troopers a damned good thrashing said storm troopers always ,apart from numerous Achtungs always shouted Donner und Blitzen or Gott in Himmel when taken by surprise.

Ref incorrect german pronunciation resulting in saying something completely different,my ex missus informed me that when I thought I was saying “dont shoot”,I was actually saying “dont Shit”

So does ‘Die, Bart Die’ really mean ‘The Bart, The’?

I’m probably totally out to lunch (where did THAT phrase come from?), but it’s my understanding that “Sacre bleu” dates back to when blasphemy was illegal in France and it’s a corruption of “Sacre Dieu” that hopefully wouldn’t get you in trouble if the wrong people overheard you saying it.