Hello,
Does anybody know if all Dupont fountain pens take international size ink cartridges like PELIKAN?

Best Regards

AFAIK, yes.

http://www.thewritingdesk.co.uk/ink_cat/cart_compat.html

Martin

Actually, that depends on the model! There are two original S.T. Dupont catridge types still available, older ones with a wider and longer mouth, and new ones which are basicly international standard size.
The older ones (Made in France) for the Classique, Gatsby, Montparnasse and Lady, the newer ones (Made in Germany) for the later models.
The old ones have a much better looking 'night blue' ink.