Odile - you seem like one great lady!
Can someone tell me what cream of tartar is in French? OH went to the pharmacy and asked for crème de tartre and they didn't know what it was. I'm guessing with a name like "Weinsteinpulver" in German "crème de tartre" may not be right.
Crème de tartre is correct.
Do what I do if I'm not sure.
Find out the google translation: Here
and then do a picture search using the translated word or phrase to confirm.
It is 'crème de tartre' but not used much and perhaps she just didn't know-
E336 or Tartrate acide de Potassium. Ask to speak to the Head Chemist of 'droguiste'. To be fair, I've only used it in the past for making playdough when the kids were little and never again.
I found it but not in an apotheke but in a droguerie. It was under 10 francs for 100 gr.
Online dictionaries say it's called: tarter brut. If all fails just give the name of the compound: Bitartrate de potassium and tell them it comes from wine making.
Cheers!