Interlanguage

If you like Lojban, maybe read the research paper "Lojban as a Machine Translation Interlanguage in the Pacific."

Trasyanka and Surzhyk are interlanguages: a Belarusian–Russian and a Ukrainian–Russian mixed language.

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.

Latin used to be the European interlanguage. Currently English widely serves this purpose.

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.