How to regenerate translated pages

A client of us has a website with two translations: Dutch and French.

A while ago we were asked to redesign this website. We only designed on the Dutch pages.

Now if we click on the flag icon and change the language to French, the old design is back – which is logical of course. The problem is that this website has over 120 pages. Approximately 80% of them are translated – so not everything.

Is there a possibility to regenerate all the pages that have a French translationed page so that they have the new designs as well? Or is there something else we can do to tackle this?