Recently, the Harry Potter novels in French showed up in my local library's collection, and I borrowed the first one to see how well my high school French has held up. I was delighted to find that my Kobo Touch already had a French dictionary, and "translate" was as simple as any other dictionary look up. I was especially pleased that the dictionary it's using (I think Merriam Webster French-to-English) included a lot of common phrases, which was quite helpful. While I did have to look up several words per page, I'll blame my high school classes: words like "wizard" and "wand" were never on our vocabulary lists.
I really enjoyed the experience, as the last time I read a French book, I was lugging around the print book and the dictionary on the bus. Kind of awkward to read, if I was unable to find a seat.