It goes way beyond dictionaries though. Once you know where you can break words, how do you know where you should break words? A simple flood fill will hyphena

It goes way beyond dictionaries though. Once you know where you can break words, how do you know where you should break words? A simple flood fill will hyphenate very enthusiastically, use suboptimal breaking points, does not consider stretching whitespace, and leads to rivers and other artifacts. Many more sophisticated algorithms suffer from the same problems. Last I used LaTeX seriously, it also produced rivers where a human using e.g. Scribus would not.