@book { DeutscheSprachinselnweltweitInterneundexternePerspektivenGermanLanguageVarietiesWorldwideInternalandexternalPerspectives,
    title = "Deutsche Sprachinseln weltweit: Interne und externe Perspektiven- German Language Varieties Worldwide: Internal and external Perspectives",
    author = "William {Keel} and Klaus J. {Mattheier}",
    year = "2021",
    publisher = "Peter Lang Verlag",
    address = "Berlin, Germany",
    url = "https://www.peterlang.com/document/1095063"
}