Interpreting is the conversion of speech (spoken language) while translation is conversion of text (written language) from one language into another. However, many people use these terms interchangeably, as in "The interpreter will translate the document out loud to the witness." (The correct term of art would be "sight translation" because the interpreter is reading a written text and translating it on sight rather than in writing. A written text is much more dense than a spoken utterance. If you want a document read to your client, the interpreter can be more accurate by doing a sight translation rather than simultaneously interpreting your reading of the text.)