interlanguage

English

From inter- +‎ language. In the language acquisition sense introduced by Larry Selinker in 1972.

interlanguage (plural interlanguages)

A language generated by a student of a foreign language that incorporates aspects of their native language and the target language.
- 2011, Anna Trosborg, Interlanguage Pragmatics: Requests, Complaints, and Apologies, Walter de Gruyter, →ISBN, page 54:
  The learner's selection from his/her store of interlanguage rules is not haphazard but systematic and predictable, based as it is on his/her existing rule system in much the same way as the native speaker bases his/her speech on the internalized knowledge of the L1 system.
A lingua franca, a common language used by speakers of different languages
Synonyms: koine, lingua franca

Latin used to be the European interlanguage. Currently English widely serves this purpose.
- 2011 October 28, Adam Thirlwell, “The Joyful Side of Translation”, in The New York Times Book Review‎^[1], New York, N.Y.: The New York Times Company, →ISSN, →OCLC, archived from the original on 12 November 2020:
  As [David] Bellos points out, those born as English speakers are now a minority of English speakers: most speak it as a second language. English is the world’s biggest interlanguage.
A pidgin or creole

mixed language

Chinese:
Mandarin: 中介語 / 中介语 (zh) (zhōngjièyǔ), 中間語言 / 中间语言 (zhōngjiān yǔyán)
Finnish: sekakieli (fi)
French: interlangue f
German: Interimssprache f, Lernersprache (de) f, Lernervarietät f, Zwischensprache f
Hindi: अन्तरभाषा (hi) f (antarbhāṣā)
Irish: idirtheanga f
Japanese: 中間言語 (ちゅうかんげんご, chūkan gengo)
Polish: interjęzyk m
Russian: интер-язы́к m (intɛr-jazýk)
Thai: ภาษาในระหว่าง (th) (paa-sǎa-nai-rá-wàang)

lingua franca — see lingua franca

pidgin — see pidgin

creole — see creole