A language island (a calque of German Sprachinsel; also language enclave, language pocket) is an enclave of a language that is surrounded by one or more different languages. The term was introduced in 1847. 
Examples of language islands:
- Chipilo and Chipilo Venetian dialect
- Griko & Grecanico
- Pennsylvania German
- Swabian Turkey
- Upper Harz
- And within Sinitic:
- Tianjinnese, a Central Mandarin variety surrounded by Northern varieties
- Ganzhounese, a Southwestern Mandarin variety surrounded by Hakka in southern Jiangxi, being one of the many Junhua
- Hangzhounese, a Mandarinic variety surrounded by Northern Wu lects, caused by the change of capital during the Southern Song Dynasty
- Zhongshan Min, a Southern Min language surrounded by Yue varieties, caused by migrants seeking shelter during the Song and Yuan Dynasties.
The predominantly French-speaking enclave of Brussels surrounded by Dutch-speaking area
Language islands in Romania
- Language and Space. An International Handbook of Linguistic Variation, Volume 1, 2009, Section "The history of language island research (Sprachinselforschung)", p.335
- Peter Auer, Frans Hinskens, Paul Kerswill. Dialect change: convergence and divergence in European languages. p. 221. "The term 'Sprachinsel' was used for the first time in 1847 to designate a Slavonic community surrounded by a German-speaking population close to Konigsberg, East Prussia cf. Mattheier 1996. 812"
- 李世瑜; 韩根东 (1991). "略论天津方言岛". 天津师大学报 (2).
- Richard VanNess Simmons (1999). Chinese Dialect Classification: A comparative approach to Harngjou, Old Jintarn, and Common Northern Wu. John Benjamins Publishing Co.