Am i correct in assuming that i need a nav webpart for each language with the correct corresponding culture code set?
I have on cms:CMSListMenu in my .Master page, and i'm going to be starting the french version of the site.
Your assumption is NOT correct. Kentico is made to use a single template and/or webpart for multiple languages. You do have the opportunity to use different templates per language but unless you need it for something very specific, it's not needed.
The webparts are smart enough to use the current language which has been selected/set on the website. There are some additional configuration options you can set like mixing the default culture with the current culture. What this means is if you are viewing the site in French and have a page in English but not French, it will display the English version and in place of the missing French version.
I'd suggest starting out with the Kentico localization documentation if you haven't already.