A study investigated the use of the interlanguage of a native speaker of Chinese using English. The subject was an art school instructor, and data were drawn from three recordings of language used in his role as teacher. It was found that despite different situations, the nature of the task determined the kind of language-learner language used. The analysis suggests that the subject possesses an English idiolect, his interlanguage, that is a full and complete system with rules and language elements adequate for his present English language needs. The subject's interlanguage shows situational variation demonstrating language variety according to context, a sociolinguistic phenomenon. One aspect of the subject's phonology showing perceptible variation (/l/ to /r/) is examined briefly, and items representing nonstandard usages in a variety of form classes (articles; prepositions; conjugated, two-part, and infinitive verbs; common and proper nouns; pronouns; adjectives; adverbs; modals; and separately, the use of "do") are summarized. A 17-item bibliography is included. (MSE)