[PCheese]

I also can’t add words, so the only way to get iOS to remember an unknown word is to add it to the address book

That is false, and this should be a good tip if you were unaware of the technique. Just add the words in Settings : General : Keyboard : Edit User Dictionary… No need to add them to the address book.

[zacharye]

That's only the case if you have certain international keyboards enabled, which is why many people don't know about it and why it wasn't mentioned in the article.