How does simultaneous interpreting work at a conference with three or more working languages?

In that case it is necessary to have more interpreting booths, always by one less than the number of working languages. Example: working languages are Czech, English and Russian, thus two booths are required: English (English, Czech) and Russian (Russian, Czech). If the original speech is delivered in Czech, each of the booths interprets into the relevant foreign language. If the original speech is in a foreign language (e.g. Russian), the English booth interprets through the so-called relay of the Russian booth (i.e. the English interpreters listen to the Russian booth’s interpretation into Czech, and then interpret their rendering into English). In some cases, direct interpreting between two foreign languages other than Czech without relay is possible.