aMockTie

Absolutely, that's a given. It even allows you to see some of the data that it has harvested from you and what it has learned about your swipe texting patterns.

But it does work well, including what OP asked for, and I expect that all keyboard apps do much of the same. How else would the devs make any money from a free app that doesn't have ads?

I've been using the SwiftKey keyboard for a while and it allows any fucking word I want to use. It's really good at learning and predicting phrases I use often, including foul language, video game terms and words, etc.