It depends on the project and the number of languages.
In the simplest case you will need at least 2 conference interpreters either for consecutive and simultaneous interpretation, unless the duration of an assignment is less than 30 minutes for conference simultaneous and 3 hours for consecutive interpretation.
Language interpretation is an extremely demanding mental exercise. In 30 minutes of simultaneous interpretation an interpreter may process more text than a written translator in 2 days of work, therefore, interpreters usually do not to work alone longer than that, because it has an adverse impact on quality.
