What is Asymmetric interpretation ?
All delegates speak in their mother tongue, but listen to interpretation into only a few languages.
In many cases, delegates understand one or (more) widely spoken languages, but do not feel comfortable speaking in it. One way to make a scarce resource (interpreters) go further is to use asymmetric interpretation.
A team interpreting back and forth between the current official languages requires 69 or more interpreters, but if you limit the active languages to three, you can get by with only a dozen or so interpreters. Delegates can all speak their mother tongue, but they can listen to only one of the three languages.
Naturally, for asymmetric interpretation to be feasible you need to be sure all delegates understand one or more of the active languages.