Not everyone who is bilingual is qualified to be an interpreter.

An interpreter who interprets correctly does not interpret words, they interpret meaning. 

An interpreter is not always a translator as well!  Interpretation is not the same as translation. The first is spoken and the latter is written. 

There are: consecutive interpreters; summary interpreters and simultaneous interpreters. 

Summary interpreting should never be used!  It does not render a precise interpretation. 

The interpreter does not make the interpretation make sense, but interprets what is being said.