interlanguage - definition and synonyms

noun [countable/uncountable] linguistics 

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/ˈɪntə(r)ˌlæŋɡwɪdʒ/
singularinterlanguage
pluralinterlanguages
  1. a mixture of two languages, especially one used by someone learning a new language, that contains features of the person’s first language mixed with those of the language they are learning