There are perhaps three hundred sign languages in use around the world today. The number is not known with any confidence; new sign languages emerge frequently through creolization and de novo (and occasionally through language planning). In some countries, such as Sri Lanka and Tanzania, each school for the deaf may have a separate language, known only to its students and sometimes denied by the school; on the other hand, countries may share sign languages, although sometimes under different names (Croatian and Serbian, Indian and Pakistani). Deaf sign languages also arise outside educational institutions, especially in village communities with high levels of congenital deafness, but there are significant sign languages developed for the hearing as well, such as the speech-taboo languages