I think the index plates do represent different countries though I don't know which but think the yellow ones may be for France. As regards the country plates, maybe different periods of time or just that you had a choice of black on white or black on your national colours.
None of the plates are for the UK, I notice, even though the 2CV was/is something of a cult vehicle over here.
EDIT: quote from UK Playmobil description:
Four different country number plates are included on the enclosed label sheet.What I want to see is a Citroen H van
https://citroencarclub.org.uk/wp-content/uploads/2019/02/hvan2-300x222.jpgThere are some models described as 1:24 or 1:25, but they are really 1:27 and so too small for PM.