Jimbo and his friend Charlie accidently discover that two of their teachers speak a foreign language. Then Charlie is kidnapped and Jimbo enlists his insufferable older sister's help to rescue his friend. It turns out that the mystery language is from a planet 70,000 light years away... The whole thing is downright silly and loads of fun. It would work well as a read-aloud. Don't be afraid of the alien words, which are not hard to pronounce. Gridzbi Spudvetch was the original title of this book, back in 1992. It looks like mouthful, but is actually quite easy to sound out.
Readalikes: The True Meaning of Smekday (Adam Rex); My Teacher Is an Alien (Bruce Coville); Ignatius MacFarland, Frequenaut! (Paul Feig).