Is sign language the same the world over?
No. There are sign language families just as there are spoken language families. In the European Union for example, 23 official spoken languages and 31 sign languages have been documented (Wheatley and Pabsch 2010). The boundaries between spoken languages and those between sign languages do not always coincide. The website The Ethnologue –an encyclopedic reference work cataloguing all of the world’s 6,909 known living languages - lists just 130 ‘Deaf sign languages’, although there are more known but undocumented sign languages.
The BSL family includes BSL, Australian Sign Language and NZ Sign Language. These sign languages are similar enough for people who know any one of them to be able to understand Deaf people who use one of the others.
On the other hand, American Sign Language and Irish Sign Language belong to the LSF (langue des signes française) family, which is unrelated to BSL, and BSL and LSF are not mutually intelligible. Often American Sign Language is used for international communication in some academic settings (possibly due to the influence of Gallaudet University in the USA, the only liberal arts university in the world for deaf students).
However, as the international Deaf community is a highly mobile community, there is also a contact variety of sign called International Sign. This is not a standardised international language but is a form of communication which draws on the context of each situation and the language backgrounds of the people involved in the contact.
Because of the visual nature of sign languages, it is often possible for two Deaf people from different sign language backgrounds to have a simple conversation using gestures and signs, even though sign languages around the world are not all the same. The strategies for communication differ from situation to situation, depending on who is communicating with whom, and what the topic is. At international conferences and events people sometimes interpret the proceedings into International Sign but this does not have the same depth of meaning and detail as interpreting into a sign language.