Mangia! is opening up a file it hasn't seen before, or has been opened somewhere else. First, we need to make sure that all the terms used in the new file are in the dictionary. To keep a "nice" dictionary, though, we try to avoid cluttering it up with a lot of terms that are very similar. This dialog just asks you to decide whether an incoming term really is different enough to justify a separate entry in the dictionary.
Why not have a bunch of similar, but not identical, terms in the dictionary? It's simple: if you have three terms for essentially the same ingredient, for example, and you want to find all recipes containing that ingredient, then you will have to specify all three of those terms to cover all the ground.
If you want to just spell something in several different ways, you can edit the dictionary entry for that term, giving the alternate spellings in the box under that label.
