I have a product list which stores English descriptions for each field.
How can i implement/architect a multi-language feature to provide the same product in French ?
You can use localization which is a .NET feature to provide resources based on the culture of the user.
This MSDN article explains localization in context to SharePoint development (http://msdn.microsoft.com/en-us/library/ee696750.aspx).
You can generate two resource lists, one in english and one in French. Then you can tell the feature to display the Strings based on the client browsers culture (eg en-us).
Here is an article from MSDN specifically about localizing a feature (http://msdn.microsoft.com/en-us/library/ee848293.aspx).
...interestingly enough, the MSDN site uses localization too. See the link above specifies (en-us, english united states), if we change it to fr-fr: http://msdn.microsoft.com/fr-fr/library/ee848293.aspx we can see the article in French too.