As Daria has already said, the third person is Nigel Farage.
They may have no headset. Schulz is a German native speaker, but also speaks French quite well (http://www.euractiv.com/section/languages-culture/news/next-eu-commission-president-will-be-a-polyglot/). This Youtube video shows that Martin Schulz is capable of discussing political issues in French. Unfortunately, we don't know whether Farage speaks, or at least understands, French at the same level.
In any case, they might be speaking French, English or German. In fact, the first link I quoted states that both Schulz and Juncker are fluent in English:
Martin Schulz, the socialist candidate and current President of the European Parliament, speaks perfect English, French and German (his mother tongue). [...]
His main opposition, Jean-Claude Juncker, candidate for the European Peoples Party (EPP), speaks fluent English, French, German and Luxembourgish (his mother tongue). He also speaks Latin, which will probably not give him a competitive advantage.
I place German as a third choice, since I'm not sure Farage speaks German.
The person on the background with a headset may not be a translator, but simply a TV journalist during a live broadcast who just happened to be there.