It's a back-to-back voting session in the European Parliament, and hands shoot up in rapid-fire succession as the roll call sounds in German: "Dafuer!" or "Dagegen!" — "For" or "Against."

Overlooking the packed hemicycle in Brussels, in booths half-obscured by tinted glass, a brigade of interpreters feed precious audio streams of the proceedings to lawmakers from 27 nations.

Humming with different languages like a modern-day Tower of Babel, the EU's institutions are the world's largest employer of interpreters — a veritable shadow army present at every summit, web-streamed hearing and press briefing.