I was using something similar on the Shopify platform, it translates everything with one click. You have to pay google a monthly fee for the number of translations, but it seemed pretty low priced. I haven't tried it yet, and I am not sure whether it does the back-end.
To translate the back-end so far what I have done is have a tab open with a vendor's view, and in another tab used the Manage Languages search function to find and translate all the obvious words that were missing or weren't correct. Weirdly some words don't show up in the search, so it's not perfect, but good for a quick fix.