I have to wonder if I am the only Esperanto supporter here...a structure where anyone can have a "home language" but there would also be the single common language.
Any single widespread "common language" will tend to diminish the home languages. A contrived language like Esperanto has no utility at all because it cannot become widespread lacking some all-powerful ruler who would decree that only it be spoken and written. The lingua franca must be naturally the language of the dominant group because that is the language that the movers and shakers, especially the commercial movers and shakers, use to move and shake. French never replaced English in England because, though the elite after 11066 spoke French, the traders did not and the French-speakers were not traders.
My ten year old daughter's education includes translating a proverb or two per "school" day out of Esperanto. Like me, she learned this scale-model hobbyist language using that marvelous computerized course created by those brazilian folks. ( http://www.cursodeesperanto.com.br/bazo/index.php?en )
I strongly recommend this course for home schooling families. It's free, engaging, and provides the excitement of easy mastery. The kids can teach themselves, and learn new grammatical structures along the way. Esperanto is a great warm-up language, predisposing the student to expect success when tackling other languages.
There are a lot more geeks speaking Klingon than there are eggheads speaking Esperanto.