"We will finish eating."
Translation:Nous finirons de manger.
Some French verbs require a "de" after them if they are followed by an infinitive. "Finir" is one of those verbs. Here is a list of some other ones: http://french.about.com/od/grammar/a/preposition_de_2.htm
There is no really English equivalent of why this is required.
Sire there is. English has a bunch of random words like this.
That's more like "We are going to finish eating". "to be going to" and "will" usually (but not always) mean the same thing, and I believe it's the same in French: the two are usually but not always interchangeable. They're trying to teach the future conjugation here, not the future construction using "aller".
Just a sorting error, most likely. The English contains "eating", which was probably picked up as a gerund by the script that sorted the sentences — or if more low-tech, then it perhaps occurred in an analogous fashion while a human was using a database and used a "*ing" wildcard to populate a set, then missed this one when manually pruning mis-sorted sentences.
One sees similar in other places, such as "The Head Office is in Italy" being in the "Medical" skill because it contains the word "head", that sort of thing.