of the World's Languages in danger, UNESCO 上索布語音系(英语:UpperSorbianphonology) 索布語字母(英语:Sorbian alphabet) 下索布語 维基百科提供如下语言版本:上索布语维基百科 Ethnologue上索布語資料(页面存档备份,存于互联网档案馆)
(PDF)于2018-06-13) Sipma, Pieter, Phonology & grammar of modern West Frisian, London: Oxford University Press, 1913 Stone, Gerald, Sorbian (Upper and Lower), Comrie
2004, 34 (2): 227–232, doi:10.1017/S0025100304001756 Basbøll, Hans, The Phonology of Danish, 2005, ISBN 0-203-97876-5 Bauer, Laurie; Warren, Paul; Bardsley