This is actually quite a bit harder than you would think. If you take a Ren'py script (that's actually what prints the words to the screen) and run it through a spell checker, it's going to throw off all kinds of bogus errors because its' going to trip over the Ren'py coding. If you write it in a word processor first then port it into Ren'py, that works easier, but adds a lot of work. I am in favor of actually proofing the finished work (or having someone else do it if that is available). Like everything, in a one- or two-man band producing a single project, there are only so many hours in a day, and something has to give, especially if the dev is committed to releasing once a month.