I have been working recently with the K2 component/plugin K2store.
As a simple shopping cart it works great, but I had a nightmare trying to get hold of any translation files.
The forum is full of people asking questions about how to translate different parts of the store into lots of different languages, but no one has uploaded any of their finished files. I posted a few weeks ago about setting up a downloads section which was promiced to be added to the downloads section but as yet hasn't happened. I imagine they are working on a 1.7 version as K2 was recently released for 1.6/1.7.
Unfortunatly forum posts aren't live until approved by a moderator so it can be weeks before you get any reply.
Anyway, I got the language file translated into French and thought I would post it here for anybody who needs it. There may be some parts missing as my store was quite heavily modified, but for most installs it should be fine.
Download: French Translation for K2store