Not every bi-lingual person qualifies as an interpreter. If the Interpreter's native language is English, and his/her second language is Spanish, such interpreter might not be qualified to interpret into Spanish.

We are very careful when we hire our interpreters so that not only do they have to be truly bilingual, but also bicultural. They must master the two or more languages they interpret, their voice has to be well modulated and pleasant, and they must be completely familiar with the subject matter.