There are several Youtube channels where people gradually train cats and dogs to use boards full of buttons (20+ buttons in some cases) to communicate their wants. It definitely seems to work in general but doesn't make the animals any less themselves... one of the funnier examples being a video of a cat repeatedly pressing the "outside" button, staring at a yard full of snow, and then stalking back and pressing the "mad" button several times. Simple compound phrases (for example, "play friend" or "love grandma") are fairly common, but any kind of actual syntax is basically nonexistent.