Alien Scream — Chris Archer

In the third book of this middle grade sci-fi series, a teen suddenly fluent in multiple languages discovers he is part alien, and someone wants him dead.
 
At Metier Junior High, Jack Raynes is usually the class clown, but lately he has one problem: mustering up the courage to ask the prettiest girl in school, Jenny Kim, on a date. That is until the day he gets hit in the head with a baseball and wakes up with the mysterious ability to speak and understand any language. Was he suffering from a concussion? Or something more sinister? When his weirdo classmates Ashley and Ethan try to tell him he might be an alien, Jack is ready to shrug them off. But then he overhears someone talking about him in a language he's never heard before, one that isn't even human. And that someone is planning to kill him. Suddenly Jack is looking to the last two people he'd ever befriend for help: Ethan and Ashley. After all, aliens need to stick together if they hope to stay alive . . .