BANZSL, or British, Australian and New Zealand Sign Language, is the language of which British Sign Language (BSL), Auslan and New Zealand Sign Language (NZSL) may be considered dialects. These three languages may technically be considered dialects of a single language (BANZSL) due to their use of the same grammar, manual alphabet, and the high degree of lexical overlap. The term BANZSL was coined by Trevor Johnston and Adam Schembri.
BSL, Auslan and NZSL all have their roots in a deaf sign language used in Britain during the 19th century. American Sign Language and BANZSL are unrelated sign languages. However there is still significant overlap in vocabulary, probably due largely to relatively recent borrowing of lexicon by signers of all three dialects of BANZSL, with many younger signers unaware which signs are recent imports.
Between Auslan, BSL and NZSL, 82% of signs are identical (per Swadesh lists). When considering identical as well as similar or related signs there are 98% cognate signs between the languages. By comparison, ASL and BANZSL have only 31% signs identical, or 44% cognate.
According to Henri Wittmann (1991), Swedish Sign Language also descends from BSL. From Swedish SL arose Portuguese Sign Language and Finnish Sign Language, the latter with local admixture; Danish Sign Language is largely mutually intelligible with Swedish SL, though Wittmann places it in the French Sign Language family. Other sources state that Swedish SL has no known predecessor. Wikipedia