attriter

One who, or that which, attrites.

One who has lost certain abilities in a language by learning and using a different language.

Attriters often experience lexical access problems, i.e. a discrepancy between what they would like to say, their communicative intention, and what they still know how to say in their L1. (Q52147493 (Q52147493) (2004), First Language Attrition: Interdisciplinary Perspectives on Methodological Issues, John Benjamins Publishing, →ISBN, page 196)