A few relevant books:

Braine, G. (2010). Nonnative speaker English teachers: Research pedagogy and professional growth. New York: Routledge.

Davies, A. (1996). Proficiency or the native speaker: What are we trying to achieve in ELT? In G. Cook, & B. Seidlhofer, (Eds.), Principle and practice in applied linguistics (pp. 145-157). Oxford: Oxford University Press.

Holliday, A. (2005). The struggle to teach English as an international language. Oxford: Oxford University Press.