Q: downloading an app in France with UK itunes

Hi. You cannot purchase an app on a different iTunes Store, and changing your iTunes ID from a country to another would mean you would loose all ability to download previously purchased apps or content on the iTunes store:

See this article for more explanation: Change the country of your iTunes Store, App Store, iBooks Store, and Mac App Store account - Apple Support

Thank you for using Apple Support Communities.

All the best,

James

You need to make an other apple id based in France to be in able to download the app.

Vous devez vous crée un nouveau apple id basé en france pour que vous puissiez télécharger cette app.