"Great Britain and the United States are two nations separated by a common language" (George Bernard Shaw). It seems strange to suggest that English readers of American texts need the help of a translator, but it's true.
What, for instance, is a "scuppernong", or a "kewpie doll"? Can you really have grasped To Kill a Mockingbird or Of Mice and Men without knowing the answers? American readers of popular texts like Goodnight, Mr Tom have similar problems, with both vocabulary and with cultural references.
Why not build an e-mail link with an American school and help one another out? www.gigglepotz.comcc.htm makes finding a partner easy.
Ask your students to write a short piece about their special interest, using as much technical vocabulary as they can. Their intended reader should be someone equally well-informed. The results will be incomprehensible to the uninitiated - skateboarders will be writing about "grinds", "ollies" and "nollies", equestrians may be discussing standing and running martingales.
Circulate the pieces within the class, asking readers to annotate the words they don't understand, then return them to the writers, who should now write an explanatory glossary. Circulate again.
In a plenary, discuss how the language you use helps define your identity, and the value of specialist vocabularies.
Schools in areas with strong local dialects could try a similar exercise, exchanging texts with students at the other end of the country.