When teaching a second language, it may be better to speak in the accent of the student’s first language rather than attempting to imitate the accent of the target language, suggests research looking at how accents may hinder or expedite language learning and comprehension.
The study that discovered this looked at how much aural information speakers of various fluencies and from a variety of ethnic backgrounds required in order to understand Hebrew presented to them in different accents:
The findings show that there is no difference in the amount of phonological information that the native Hebrew speakers need in order to decipher the words, regardless of accent. With the Russian and Arabic speakers, on the other hand, less phonological information was needed in order to recognize the Hebrew word when it was pronounced in the accent of their native language than when they heard it in the accent of another language.
So it seems that British football manager Steve McLaren was helping English learners when he gave his infamous interview in the Netherlands following his move there!