Interpreting and translation are two closely related linguistic disciplines. Yet, they are rarely performed by the same people. The difference in skills, training, aptitude and even language knowledge are so substantial that few people can do both successfully on a professional level. On the surface, the difference between interpreting and translation is only the difference in the medium - an interpreter translates the spoken word, whereas a translator interprets the written word.
There are several types of interpreting: Consecutive, simultaneous and public service interpreting being the main three.
In consecutive interpreting, the interpreter waits for the speaker to finish a sentence or an idea, and then renders the speaker's words into the target language. Generally speaking, the more formal the setting, the longer the segments should be. Interpreters are trained in special note-taking and memory techniques that enable them to render passages as long as 6-8 minutes faithfully and accurately.
Consecutive interpretation is best suited for situations involving a small number of people, or where a personal touch is required. Examples would be business meetings, press conferences, interviews, teleconferences, or any type of one-on-one exchange.
In simultaneous interpreting, the participants wear headphones, and the interpreter renders the speaker's words into the target language as he or she is speaking. Because of the tremendous level of concentration required to perform this type of interpreting, simultaneous interpreters always work in teams of two, working for about 30 minutes at a time. Usually, the interpreters work in a sound-proof booth that enables everyone involved to focus on their work without the distraction of hearing another language.
Because this mode of interpreting saves time, it is preferred for conferences and meetings in which a great deal of information has to be conveyed. The use of audio equipment also means that there is no limit to the number of people who can participate. It is often used at the EU & UN, for example.
Public service interpreting is also known as liaison interpreting, where the interpreter works both ways, in contrast to consecutive and simultaneous interpreting where the interpreter only works in to their mother tongue. Public service interpreting is used in court rooms, police stations, medical situations and in certain business situations that involve two or three people.
So what are the different skills that are required?
The differences in skills are arguably greater than their similarities. The key skills of the translator are the ability to understand the source language and the culture of the country where the text originated, then using a good library of dictionaries and reference materials, to render that material clearly and accurately into the target language. In other words, while linguistic and cultural skills are still critical, the most important mark of a good translator is the ability to write well in the target language.
Even truly bilingual individuals can rarely express themselves in a given subject equally well in both languages, and many excellent translators are not fully bilingual to begin with. Knowing this limitation, a good translator will only translate documents into their native language.
An interpreter, on the other hand, must be able to "translate" in both directions on the spot, without using dictionaries or other supplemental reference materials. Interpreters must have extraordinary listening abilities, especially for simultaneous interpreting. Simultaneous interpreters need to process and memorise the words that the source-language speaker is saying now, while simultaneously outputting in the target language the translation of words the speaker said 5-10 seconds ago. Interpreters must also possess excellent public speaking skills and the intellectual capacity to instantly transform idioms, colloquialisms and other culturally-specific references into statements the target audience will understand.