Two aspects to the question...

Firstly user feedback is overwhelmingly positive except for the 'Next' button - they say why have it. as it goes to the next question as soon as you click an option. It would be better for my application if I could rename it 'Skip'.

But where is it defined?

I've done a grep search on the component, but cannot find it!

Also, I'm trying to insert French translation into the Start button using Démarrer, the e acute does not render correctly in teh font and using the html code é breaks the button.

In French, I get the translation of Précédent (Previous) working OK, but I can't find that either in order to see how you got the accents without breaking the button.

We chose the word 'Next' because it pairs nicely with 'Previous'.
Also, auto-next is a selectable option, that can be turned off. So it is not always true that clicking an option equates to going to the next question. It is also possibile to return to the previous question and then move forward again.
Hence we deemed useful/necessary to have both buttons.

The translations are into files:
(frontend)
components/com_productfinder/language/en-GB/en-GB.com_productfinder.ini
(backend)
/administrator/components/com_productfinder/language/en-GB/en-GB.com_productfinder.ini
/administrator/components/com_productfinder/language/en-GB/en-GB.com_productfinder.sys.ini

To create your own translations you need to:
- copy:
components/com_productfinder/language/en-GB/en-GB.com_productfinder.ini
as:
components/com_productfinder/language/fr-FR/fr-FR.com_productfinder.ini
- edit the file you just copied
- do the same for the backend translation (if at all required)

Here's the link to the official Joomla guidelines for creating your own translations:
docs.joomla.org/Technical_Guidelines_for_Translation