On a budget, Planet Word still earns its price.
Free (suggested ~$15 donation, reservation)
DC's sleeper-hit museum: you talk, sing, and play your way through 50-odd interactive exhibits about how language works, and a 22-foot 'speaking willow' tree whispers greetings in hundreds of tongues. The catch: it's hands-on by design, so on busy days the timed exhibits back up and you'll wait your turn at the popular stations.