Sign Language Interpreter sacked because of race

Keith Wann, a sign language interpreter working in American Sign Language (ASL) is suing a theatre accessibility programme after claiming he was fired from the Broadway production of The Lion King for being white.

It is alleged that it was a form of appropriation for a white person to be signing for a black character.

What other attributes of an interlocuter will interpreters be expected to manifest before being granted access to gainful employment? Deafness?