In Lewis's world, I think it was expected that any reasonably educated person had studied Latin and didn't need a translation. He must not have foreseen the gradual elimination of Latin from the curriculum in most schools (at least here in the US--I don't know how it is in the UK).
I had Latin in high school and went on to pursue a Classics major. My high school was the only school in the district still offering Latin when I was there... it got rid of the programme five or six years later.
My daughter attended a Classical Christian school when we lived in Colorado, and would have started Latin in second grade if we had not moved. Sadly, enrollment was not enough for the school to keep going and I've heard they had to close. I would love to find a Classical Christian school near where we live now, but there's no such thing within a reasonable distance. Katie thrived there in first grade, and was very sad when we had to move. Someday I have to get in gear and start teaching her and her siblings Latin again.
I can't guarantee the accuracy of it, but I found this freeware when I did a google search for Latin Translator.
http://www.sofotex.com/Latin-Translator ... 23697.html