On Thursday, the historical 1869 landmarked school will reopen, entirely refurbished and partly restored to its original condition, and once again serving something close to its original educational purpose. Planet Word, a museum devoted to language, is the new occupant, and it will pay the city $10 a year on a 99-year lease. The purpose of the $60 million museum, according to its gallery map, is to “inspire and renew a love of words, language, and reading in people of all ages.”