Language interference is a phenomenon investigated within second language acquisition and applied linguistics, referring to the influence of one language system, typically a learner's first language (L1), on the learning or use of a second language (L2). This concept examines the nature, manifestation, and consequences of cross-linguistic transfer across linguistic levels (e.g., phonological, grammatical, lexical), analyzing both facilitative (positive transfer) and disruptive (negative transfer, often leading to errors) interactions between languages, thereby providing crucial insights for explaining learner language development and informing pedagogical strategies.