An interlanguage is an emerging linguistic

Linguistics

Linguistics is the scientific study of human language. Linguistics can be broadly broken into three categories or subfields of study: language form, language meaning, and language in context....

 system that has been developed by a learner of a second language

Second language

A second language or L2 is any language learned after the first language or mother tongue. Some languages, often called auxiliary languages, are used primarily as second languages or lingua francas ....

 (or L2) who has not become fully proficient yet but is approximating the target language

Target language

Target language may refer to:*Target language, in applied linguistics and language education, the language which a person is learning, also called second language*Target language, in translation, the language to which a source text is translated...

: preserving some features of their first language

First language

A first language is the language a person has learned from birth or within the critical period, or that a person speaks the best and so is often the basis for sociolinguistic identity...

 (or L1), or overgeneralizing target language rules in speaking or writing the target language and creating innovations. An interlanguage is idiosyncratically based on the learners' experiences with the L2.